This article explains how to view an attached image directly in an incoming Yahoo Mail message without downloading the file. This is only possible in the latest version of Yahoo Mail, not Yahoo Mail Basic.

You can display images directly in an individual email, or adjust your settings to always see them in all emails. Here's how.

Select Show images in the body of an email to view them in this case, or select Always show images to quickly display all images.

To enable this through Settings, select Settings in the top right corner.