Here's what I did,
Applied online, while doing so if you check box that you'll mail supporting docs, then your printout will say so.
Go to Support Center, they'll take your pic, one fingerprint, and will stamp that printout (proof that you appeared).
I photocopied that stamped printout, also placed cover letter printout on top of all supporting docs.
I Included following:
Approval Notice of 140
Receipt Notice of 485
Stamped proof of appearance for photograph
If you are applying for 2nd/3rd EAD, also include copies of previous approval Notices/ EAD's
No need to send pics, or check since you already paid online.