If you haven't yet found the portrait ID's for some of the hidden portraits in M25, here goes a quick list of a few:
6239 - DE JJ Watt
6195 - WR Larry Fitzgerald
6220 - HB Adrian Peterson
6206 - WR Calvin Johnson Jr.
6199 - TE Rob Gronkowski
6224 - CB Darrelle Revis
6241 - LB Patrick Willis
6235 - OT Joe Thomas
6187 - QB Tom Brady
The "hidden" photos are located between 6185 (Champ Bailey) & 6242 (Charles Woodson).