Should a badge be awarded for adding images to a question or answer, like there are for using other aspects of a Stack Exchange web site such as editing a post?
If ever implemented, then instead of awarding it for the image, please award it when the user sets a custom alt text.
(He, that's your feature request too! Maybe the encouragement for setting the alt text could be a badge then?)
Seriously though: Using a badge to make people aware of the feature is a honourable idea at first, but the image feature is not essential for providing good content. Many SO users get by without ever using an image, and there are many ways of harming the site through images. Therefore, I think this is not a feature that should be explicitly pointed out.
If you award badges for images, they are awarded for good and bad images.
If you have an answer with a good (appropriate) image it will be awarded with upvotes.
Besides if you start awarding images, why not awarding links, or pieces of code. Its all part of the content and the content is responsible for the up and downvotes.