What you can do with pencil drawn pictures
When I want to add some color to the picture, I prefer to use computer for it. I scan pencil drawn sketch and begin experimenting...
What I noticed after uploading both black&white pencil drawings and their colored variants to DT is that colored pictures sell better, and sell fast! Sometimes even after a few hours being online when sketches have to wait for a buyer much longer.
So I come to conclusion: it's a good idea to make colored variant for every pencil picture. Several different color variants and maybe some vector ones would do only better.
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Photo credits: Makarova Olga.