1. Evidence: a copy of the actual photograph or document is included.
2. Description: Don't assume that USCIS will immediately understand the significance of the evidence. Include a caption, or a description of the document.
3. Context: Facts are nice, but without something explaining how the fact fits with the petition or application, it will not be persuasive.
A big mistake commonly made is to submit part of the requested information, with the idea of sending the rest later. Don't do this. Gather all of the requested materials, include an exhibit list, and send it all in one package. That will satisfy the USCIS.