This post has been updated with a clearer screenshot from Sonic Retro's coverage of the subject.
The shot that interests me the most, however, is this one:
That blobby thing to the left of Sonic is
almost certainly the butt-chinned baddie from the lower right of this concept image:
Yes, it's purple with yellow gloves in the concept art but blue with red gloves in the screenshot. But bear in mind this is the matter of a simple palette swap, from line 1 to line 2:
There may have been more than one version of the baddie, or maybe they hadn't decided on which colour scheme to use yet. But I digress.
I find this discovery pretty gobsmacking. Yes, I've been aware of the concept art for a long time, and that it took the team a while to really nail down what Sonic and his world were going to be like. But to see an actual screenshot of the running game (albeit a prototype) that predates the concept of badniks - well, it's awesome, but also sort of terrifying. We came this close to living in a world where Sonic did battle with proctological monstrosities instead of the metal menaces we've come to expect.
Maybe someone from Sonic Team played Mega Man and was inspired to give Eggman a mad scientist makeover and an army of robots. Whatever the cause, thank goodness they did. Sonic narrowly avoided a long career of being groped and probed.