When you are uploading or hosting images for use with EBS be sure they are in the JPEG, GIF or PNG file format.  These are the only supported web image formats.  Be sure that the file name does not contain any spaces or punctuation (A-Z, 0-9 only) and contains a .jpg, .gif or .png file extension.

If you are hosting your own image, be sure that the HTML IMG SRC reference points to the full URL.

Correct Example:

<img src='http://asset1.zendesk.com/system/logos/0005/0433/newlogotrans.gif'/>

You should be able to copy and past the full URL: http://asset1.zendesk.com/system/logos/0005/0433/newlogotrans.gif into your web browser.  If the image displays within the browser then the image should load properly within your email.  If it does not display within the web browser, then the URL is incorrect, or there is a file permission issue on the web browser.

Incorrect:

<img src='/newlogotrans.gif'/>

If you are using an external application to design your email the images will either have to be uploaded to EBS or hosted on your web server. The images will have to be placed using the online EBS editor if uploaded, or the HTML IMG SRC references will have to be updated with the full URL for the image location if hosted.