I don’t think you can say that with surety. That’s a massive erection here for one thing, and an at least semi-flaccid penis in the avatar, and the point of view doesn’t allow for much in the way of comparison of specific features (like the lateral vein tributaries seen in the av). Whoever it is, both pics are of really big dicks. They look sorta similar. But I do think the one in this post does look pretty familiar, like something that’s maybe been around on the web.