I want to upload a picture to one of my questions, but I keep trying different forms of the picture, but none of them work.
Failed to upload image; the format is not supported
I have tried PNG and JPEG. What formats are acceptable?
PNG, JPEG, GIF are all supported formats, your particular images were likely not encoded properly.
I would suggest trying to open them in MS Paint (or any other basic image editing software) and then saving it through there.