Sounds like they are actually resizing it. busy.org either css resizes it or saves a downsized version and if you click on it, will open the full size in an overlay for you. Steempeak (the one I use most regularly) has a less intuitive right click view image kinda setup but full image is still nondestructively accessible.

I haven't used steemit for a while, people keep going on about how it's the flagship product and all but I have vague notion that they basically only had a website for people to sign up on because they needed one at the time (being the one and only and all) and really wanted other people to do the front end stuff while they concentrated on back end stuff.