fitztrev

Comment Image Embedder is a very simple plugin that, once installed, lets your visitors add an image to their comments.
It’s rather common for a WordPress user to ask how visitors can embed images in the comments section of their blogs.
This plugin will add a link just below the comment box that a user can click on. When clicked, a prompt will appear for the user to enter the URL of the image. It will then be added to their comment.
Trevor Fitzgerald 
http://trevorfitzgerald.com/

Comment-Images

Comment Image Embedder is a very simple plugin that, once installed, lets your visitors add an image to their comments.

Scott Werner

By default, WordPress links images to themselves. A user sees that the image is a link, clicks it and they are then taken to a page of just the image. Then they click ‘back’ in their browser or move on to another site.
You could manually remove the link, but that is a pain. Plus, when handing sites over to clients they shouldn’t have to remember to remove it to have a great functioning site.

No Image Link

Defaults the Image Link option to 'none' when adding a picture to a page or post.

Comment-Images vs No Image Link