Can I post just a photograph of the part I want to source?

A design, CAD file and drawing with technical details is required when sourcing on MFG.com. Since you are asking a supplier to use your RFQ to prepare a reasonable, accurate quote, the files attached to your RFQ is all they have to base their quote on. The more detailed your specifications and designs are, the more accurate your quote will be, and the better a supplier can meet your needs.