Do you use Yahoo! Mail as your E-mail provider? As a rule, Yahoo doesn’t allow images to be downloaded automatically, except for those from people in your contact list. This is all in an effort to increase security, but for anyone wanting to live on the wild side there’s a way you can turn it off.
Just log in to your Yahoo! Mail account and click on Options (in the upper-right hand corner) then Mail Options.
In the next screen click on “Spam” in the left pane, then put a dot next to “Always show images, except in Spam folder“.
Hit Save Changes, and you’re done! Just repeat these steps and re-select “Show images only from contacts” if you ever want to go back to the way things were.