Dafuq, its real. This is such a weird thing to do. And it you open the image full size, the black rectangle is gone.

OMG these are fun!

I ran out of time and couldn't solve the last two.

where did you get that? i want one!

I wonder if it’s some kind of tracking watermark like printers have.

I misunderstood your statement. I thought you meant a solid black rectangle along the entire bottom of the image. The picture you posted shows me that you mean a transparent black rectangle in the bottom left corner. The edge of that rectangle lines up exactly with where OPs apparent cleavage appears. The black shirt and their picture hid the rest of the effect. Thank you for helping me see it.