This artist often does this, where on a work-in-progress they take picture of their computer monitor and post it on the Twitter feed. It seems like it would be easier to just take a screen capture. The visible lines of the screen pixels, reflections on the monitor, etc. usually degrade the quality of the image below what seems to be the threshold for an upload to get approved, so I usually don't try to upload them.

Artists are gonna art, and probably aren't that technically oriented. I also wonder the same about artists that take pictures of their art on paper, and can't even be bothered to do a proper job at cropping. I mean, how hard is it to download a free image manipulation software and do some rudimentary cropping?