Is it possible to create a picture using a hex editor?

Answer 1

Absolutely. If you edit the contents of a bmp, raw, or even uncompressed TIF file, you can make any picture you want. In theory, you could also edit a jpg file this way, but it would be much, much, harder.

Answer 2

That to me is like asking if you can build a house with a pine cone?

Yes you can, if you plant it let it grow, cut it down, and make a house, but it isn't the easiest way, and may not have the best results.

Why you are trying to do image editing with a hex editor? If you are trying to make your own graphic program or are you trying to do something else?