The image itself isn't stored as part of the blockchain; the blockchain just stores a reference link to the image. Still, if you're uploading images directly into the posts those images are stored on a server users have no control over after the editing period is over. That could be a problem.

However, there's no reason you can't store the images you use on your own server or with an image hosting service like Imgur. If there's an issue with an image down the line---perhaps because someone claimed an image was available under a license that the actual creator had not granted, or if the creator is disputing your use of their IP under what you consider fair use---you can delete the image at will. Some services, and definitely your own server, will allow you to change the image file at the immutable referenced location to something else after the post editing period is over instead of just deleting the image outright.