By default, Yahoo! Mail prevents the automatic download of images in email messages (except messages from your contacts) as a security measure. You can override this feature and download all images that come to your Inbox.
1. Go to Yahoo! Mail and login to your account.
2. Go to the upper-right corner, click Options and select Mail Options.
3. In the left pane, select Spam.
4. In the right pane, go to the SpamGuard section. Select the Always show images, except in Spam folder radio button.
5. Click Save Changes.