Can You See Me?

An estimated 95 percent of all commercial e-mail messages are sent in HTML or in a multipart (combined HTML and text) format. Most e-mail includes at least a single external image, even if it's the open-tracking image, a clear, one-pixel GIF image used to track whether an e-mail has been opened.

The primary reasons behind image-blocking features are to enable users to prohibit pornographic images from loading and to prevent spammers from knowing if users open their messages. Gmail, for example, states: "Gmail disables images sent to you to protect you from unknown senders, like spammers, who use images and links to verify that your email address is real."

Image Blocking by Major ISPs & E-mail Clients
Blocking Issue	AOL Versions 6.0-9.0	Gmail	Hotmail	Yahoo	Outlook 2000/ XP	Outlook 2003	Outlook Express w/SP2	Outlook Express w/o SP2
External images are blocked by default	Yes	Yes	No	No	No	Yes	Yes	No
User controls image-blocking settings	Yes	No	Yes	Yes	Yes	Yes	Yes	Yes
User clicks link to enable message's images	Yes	Yes	Yes	No	No	Yes	Yes	N/A
Images enabled if sender is in user's address book/buddy list	Yes	No	Yes	No	Yes	Yes	Yes	Yes
Images autoenabled if sender is on ISP whitelist	Yes	N/A	Yes	No	N/A	N/A	N/A	N/A
Alt tags displayed when images disabled	No	Yes	No	No	No	No	No	N/A
Preview window featured included	No	No	No	No	Yes	Yes	Yes	Yes
Note: SP2 = Service Pack 2 upgrade for Windows XP
Source: EmailLabs, 2004