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By: Casey Grimes on September 20th, 2018

Images in Email: The Best Practices Guide

Photo of a marketer in front of a laptop and a mobile phone in one hand so that they can test the image quality of their email campaign.

Odds are if you’re using marketing automation, you’re using email. Odds are if you’re using emails, you’re using images in those emails.

Some of the most common questions and issues we’ve seen pop up over the years here at DemandLab focus squarely on image content in emails and making sure designs are set up for success.

While image editing and work can seem daunting to marketers—especially those without a graphic design background—thinking through your email images with a set of concepts like image size, format, layout and placement can take your emails from “just OK” to the envy of your emailing peers.

What dimensions should my images be?

Supporting high DPI devices

High DPI or “Retina” devices have become increasingly common in the past several years; the basic idea is that screens on these devices have a higher pixel density than previous standards, resulting in sharper and clearer images. For example, here’s two screenshots of a standard display and a high DPI display:

The blocky pixels you see on the right are eliminated by having the higher density of pixels on the screen. Odds are if you’ve purchased an iPhone (or an Android phone in the past 3-4 years) you actually have a high-DPI device. This technology has also been implemented in tablets, products like the MacBook and iMac, and newer monitors such as Dell’s UltraSharp and LG’s UltraFine series. Paying attention to high DPI devices is especially important for emails, since more than half of all emails are opened on mobile phones.

Creating email images that work well with these newer displays for crisp output is straightforward: simply make the image twice the size you intend to display it, and you can provide high DPI support. For example, if you want to display an image that’s 250 pixels wide and 100 pixels high, you would simply create an image that’s 500 pixels wide and 200 pixels high (twice as large on both sizes) and then use HTML tags to force it into the size you want, like so:

HTML tag for images to force size to 250 x 250 pixels

As an example, take a look at the two images below: one is scaled 1x (the image size is the exact same size as what’s displayed) and one is scaled 2x (the image used is twice the size as the displayed area.) These screenshots from iPhone 8 illustrate what happens:

If you look at the DemandLab logos on the left, you’ll see they display in a blurry manner, especially in curved areas, compared to the 2x logos on the right. As a result, DemandLab strongly recommends always sizing your images to exactly twice the size you want the image to display as.

Now, you’ll notice that we said the image should be “exactly 2x.” A common trap email marketers fall into is just using large images in general rather than images that are sized specifically for an email. Let’s say, for instance, you want to share this really cool image of a hummingbird in your email newsletter.

Very beautiful and very detailed! Our email list is going to love it.

In my email template, we have a predefined high DPI image size that will allow the image to take up 50% of my email’s layout: so in this case, 540px wide, but scales down to 270px.

To demonstrate, we’ll put two of these modules in with the hummingbird as the image: one that’s the native size of the image we saw above, and one that’s sized down for the email. You’ll see that in Marketo, the images look functionally identical:

When we look at these images on a Retina iPad, though, we can see the difference quickly:

If you look at details such as the reflection in the hummingbird’s eye or the individual striations in the bird’s feathers, you’ll see the image that was sized down actually looks sharper! This is because devices have to dynamically scale down images that aren’t 100% or 200%, and such you get arbitrary calculations (like 389% in the case of the original hummingbird image). This creates the blur you see: the device is trying to make things work but can’t apply proper sharpness. As such, it’s important to always size your images to fit the area you’re working in.

How do I resize my images for email?

Ideally, using a tool such as Photoshop makes image resizing a breeze, with the ability to edit image sizes, canvas sizes, and crop to certain image sizes out of the box—but not everyone has access to Adobe products. A great alternative we recommend using is Paint.NET for Windows, which is free whether it’s used for personal or commercial purposes. Step-by-step instructions are available for resizing images are available below:

Do note if you are on OS X and don’t have access to Photoshop, you may want to consider Pixelmator Pro, but we here at DemandLab have yet to do a full test of the product.

What format should I save my images in?

When it comes to email, there are three main image formats you’ll want to use: JPG, GIF and PNG.

JPG: The JPG/JPEG format was developed with photography in mind and as such is your best bet for anything with photos. However, the tricks that JPEG uses to make photos look good while saving space can make things like text or shapes look blurry; you should use PNG instead in these cases.

GIF: GIF is still the format of choice for animated images (animated PNG support is poor). Do note that if you are mailing to audiences with animation that not all clients support animation itself–most notably Outlook. As a result, you’ll want the first frame of your GIF animation to be the “fallback” image you’d like to display.

PNG: Images that are drawn on a computer (such as screenshots or digital art), as well as anything that needs transparency—all modern email clients, including Outlook 2007 and up, support 24-bit PNG transparency. The only exception to this is Lotus Notes 7 (which, while supporting PNGs, does not support transparency).

SVG: If this was an “images on websites” post, we’d be strongly advocating for converting any EPS or vector-drawn images to be displayed as SVG. Unfortunately, email support for SVGs is poor at this time; as such, anything that would be SVG in your email should be converted to PNG.

BMP: Listen, there’s only one BMP we’re recommending for email, and it’s not an image format.

The pixel sizing of an image is only half of the equation when it comes to images in email, though: you also need to consider the file size of the image itself. Over time, the average total file size of email images in newsletters has grown from about 300KB on average to a little over 550KB:

(h/t to René Kulka for his analysis of ~1700 newsletters/week over time)

While this size increase means that your emails have some wiggle room in terms of image size, you’ll want to consider the earlier statistic we mentioned about over 50% of email opens happening on a mobile device. Because coverage can be spotty and you never know who’s stuck on 3G, you’ll want to condense your image file sizes so they are small but effective. Lossless image technology takes your image files and finds ways to compress them so that they do not lose quality, but still have a smaller file footprint. I personally use FileOptimizer for Windows machines and ImageOptim for OS X.

Pro Tip: If you’re using FileOptimizer, when you first open the program, go to Optimize -> Options and select the “Appearance” tab. Check “Hide Ads” and save.

Running your images through these programs will decrease file size while keeping quality intact. Typically, PNG files get the most out of this process (for example, compressing the DemandLab logo for email goes from 4.7kB from Photoshop to 1.6kB using FileOptimizer, a 66% decrease) but all file types will see some benefit from being compressed.

Using images in email: best practices for success

When it comes to actually placing images in your emails, there’s some best practices you’ll want to keep in mind for optimal use. Let’s say, for example, you’d like to cover a video of the Oregon Zoo’s series where they introduce small goats to other zoo animals (seriously, it’s worth the click-through) and want to use this image:

There are several things to consider for using images in your email:

  • Always, always, always use alt text—and make it meaningful. For every image you have, you’ll want to define alternate text—that is, a text description that describes what the image is trying to convey. That means if you’re going to use an image, you need to provide a meaningful alt tag.

    • Do not: just populate the alt tag of the image as “goats_image.jpg” or something similar, like “600px wide image”. This helps no one other than you, the email designer.

    • Do not: populate the alt tag of the image with something like “enable images to see these cute goats!” The people who need alternative text the most don’t have the opportunity to turn their sight on.

    • Do not: just give a short explanation of the image without context, like “two goats looking at a seal”. While this describes the image, it’s not providing an extra layer of understanding.

    • Do: give a robust description, such as “Ruth and Sonia, two young pygmy goats at the Oregon Zoo, are shown on leashes near the zoo’s Stellar Cove exhibit viewing a harbor seal” to make the context of the image clear.

  • Image title tags are less important than alt tags. Though title tags can be useful for providing details on an image, they’re generally discouraged in favor of alt tags for accessibility purposes. There’s no harm in repeating your alt tag content in your title tag content; just remember to use alt tags as your primary descriptor of an image.

  • Think about your images with accessibility in mind. There’s more to accessibility than just images (a larger topic for another day!) but you’ll want to particularly consider contrast and coloring in images for those with colorblindness or those looking at your email on a device outside where there may be glare from the sun. DemandLab recommends installing the Funkify extension for Chrome to test how your images may look to various visually-impaired audiences—people who may have blurred vision, partial vision loss, red/green color blindness, and so forth.

  • Use images judiciously. Even though goats meeting a seal may be a big enough deal to be the focus of an email, you’ll want to manage your image use to avoid potential spam issues, as image-to-text ratio is a common spam determination factor. Generally, images should be no more than 25 to 50% of your email’s overall content.

  • No base64 encoded images. While base64 encoding and other data uris are picking up steam in the world of web design, they’re a solid no-go for email. Stick to referencing image files in emails rather than trying to use strings to make up for files.

  • HTTP vs. HTTPS can make a (minor) difference. Given that Google is making a large push to get most of the web to the HTTPS standard in 2018, you may find yourself serving images from HTTPS rather than HTTP. This provides a (very, very) minor positive factor when your email is being determined for spam, but this also means you may run into cases where Outlook users cannot see the image because of an Exchange setting labeled “Do not save encrypted pages to disk.” This setting prevents HTTPS-encrypted images from being seen; while this is increasingly being disabled by sysadmins, it is a consideration to keep in mind. HTTPS images can also cause issues on older clients like Outlook 2003 and earlier due to a lack of SSL/TLS support.

  • When using Marketo Email Template Syntax, try to use < div > over < img/ >. If you are a template designer, try to always err on the side of using a div tag wrapping an image with the mktoImg class, as this allows the end user to add links to the image. The only time using an image tag with the mktoImg class is preferable is if you need the image to be explicitly inline; all Windows versions of Outlook will not respect images in div tags as being inline even with !important overrides.

Finally, remember: an email is not a print mailer or brochure

With all these guidelines in mind, an important final note is to remember that even though email uses a lot of design elements, it’s a totally different beast than traditional print design. Email readers will not visually track through your content in the uniform way they do with print pieces, and often is consumed differently—how often do you find yourself just reading the subject line and first few lines “above the fold” of an email before deciding whether to read further or just hit archive/delete?

This also means that visually, your email will not have the same pixel-perfect design that print items have because of the inherently interactive nature of the content you’re creating. This can frustrate designers (and even executives) because email can’t “look as good” as a brochure or flyer. However, at the end of the day, having 100% visually flawless emails isn’t your goal as a marketer; it’s to drive results and revenue. Know when to pick your visual battles and when it makes sense to simplify a design.

If you or your team would like to get a deep dive on how to best use images, along with other email content, for revenue impact and success, consider getting customized martech training—we’re happy to cover anything and answer your questions at length.