Have you ever wondered whether the beautiful images you include in your email messages actually get seen? The answer might surprise you. A lot of recipients block images in HTML formatted messages either by personal preference or by default email client settings. Some people block HTML messages altogether

A study by Merkle in 2009 stated that only 48% of recipients saw email images automatically. When you consider the sheer volume of email in today’s inboxes, it makes sense for users to skip image download to save time when scanning messages in the preview window.

While most email platforms can provide metrics on delivery, clicked to open, clicked but did not open, and even HTML versus text opens, when it comes to determining the overall number of opens with image versus without, the math gets a little fuzzy. There are ways to theorize the results, but these are based on assumptions and provide no hard facts. So what do we know?

Every email client has its own default settings for the display of images. Most clients include simple on/off switches for images. Some have conditional settings based on factors such as known senders. A quick look at versions of common email clients such as Outlook, Apple Mail, Thunderbird, AOL Desktop, Lotus Notes; webmail clients such as Outlook.com, Yahoo! Mail, Gmail, AOL Webmail; and mobile clients like iPhone, Android, Blackberry, and Windows Mobile reveals that only four show images by default. The rest render text by default with an option to display images from trusted senders.

Armed with this knowledge, the best approach for marketers is to expect the best and prepare for the worst. That means following best practices for designing your email with images while assuming those images will be turned off. Some basic best practices for messages featuring images include:

Retains readability in common email clients with images turned off
Readable for recipients with visual disabilities and navigable for those with mobility disabilities
Small overall file size for recipients using mobile devices or slow connections
Deployed to a permission-based subscriber list
Meets CAN-SPAM Act requirements
That covers the best case scenario, but what about the worst? In order to prepare for recipients with images turned off, try the following:

Begin your email with HTML text or ALT text to ensure the recipient sees your message in the preview window even if images are turned off
Use ALT attributes on all images to provide text where images are absent
Use captions for contextually key images
In addition to following best practices for email with or without images, there’s one more thing you can do: Become a “known sender.” Almost all email clients enable recipients to automatically view images in messages from “known senders” – those who are included in contact lists, address books, or white lists. To ensure your subscribers include you as a “known sender” consider the following:

Ask your subscribers to add your address to their address book at the point of sign-up
Enable a double opt-in subscription process that includes a plain text confirmation with a request to add your address to their address book
By following these simple suggestions marketers can improve the odds that their product and promotional images, illustrations, and charts get seen when recipients open their email.