It used to be that in order to see images sent along to you in iChat, you’d open up the File Transfers window, click on the graphic, and hit the spacebar on your keyboard to see the image full size, just like you can in the Finder or Open/Save dialogs.
If you’ve migrated to Mountain Lion, however, you’ll know that iChat is no longer, and the replacement app, Messages, has a File Transfers window, but Quick Look won’t work in it any more. How do you see your images full size within the Messages app, then? Lucky you, we’re here to tell you.