Ron Blaisdell, a member of the Email Marketer’s Club, recently tested whether embedding images in HTML emails could be an answer to image blocking. He shared the results of this test on the Club’s forum and I thought I’d share them here as well:

Over the years, a number of folks have asked if "encoding" the images
in their campaigns would allow more people to see their campaigns, with
images, and not have them blocked by the various email clients.

Using a web application to encode an image in base64, allegedly will allow images to be displayed and by-pass image blocking.

Using a base64 encoded image, you end up with an image tag that looks something like:

[img src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAADIA…" alt="Encoded Image"/]

I created a custom xhtml campaign, encoded a single image, and sent this to my testing list. The results:

Gmail: Displays only alt text
Hotmail: Displays a grey square, not the image, and no alt text
MS Live Hotmail: Same as Hotmail
Outlook 2003: Display a broken image, with alt text displayed
Outlook 2007: Same as Outlook 2003
Yahoo Classic: Displays only alt text
New Yahoo Mail: Same as Yahoo Classic
AOL: Displays alt text
Hosted Gmail: Displays alt text
Thunderbird: Displays alt text
Outlook Express: Displays broken image, with alt text displayed

Apparently, since spammers have been using the encoded image trick for
some time, email programs have adapted to stop their display!

Therefore, encoding images for campaigns is not worth your effort, and normal image linking, is the best solution.

(As an aside, this was tested using multiple ESPs, and the results were consistent, regardless of ESP used.)

Thanks for testing and sharing the results with us Ron!