Art is not a thing; it is a way. – Elbert Hubbard
Here are a couple of Marvel blank variant covers I whipped up recently. Blank variant covers are real comics, with the regular insides. The only difference is the cover is blank on the front and back.
Here is an Uncanny X-Men #1 with a pencil sketch of Deadpool.
And an X-Men #7 with a colored sketch of Magento.