In the case of a player who has played on multiple teams in a single season, here are a couple of options for player photos.
Each players UID number allows for expansion beyond six (6) digits. Therefore, in the case of multiple players on multiple teams in the same season, you can add an additional number to the existing UID to distinguish the player/team combination. For example in 1969 Ken Harrelson played for Boston and Cleveland. His uid is 15383. Keep that UID for his Boston record and through the Organizer, change his Cleveland UID to 153831 (adding a single digit to the existing UID).
Name his Boston photo 15383.jpg and then name his Cleveland photo 153831.jpg . Drop both images into the appropriate sized folder playerpics folder within the 1969 season database folder. Now, when his Boston record is used, it will display his Boston photo and when his Cleveland record is used, the game will use his Cleveland photo.
The downside of this method is that if you want to import stats into the Encyclopedia or use the Migrate function, you will have to remember to change Harrelson's UID number back to its original 15383.
The second method is to change the player photo as changes occur during a season. Using Harrelson as an example, you might have a photo of him with Boston and one with Cleveland. Since he plays first with Boston, let's name his Boston photo 15383.jpg. Name his Cleveland photo 15838A.jpg. Drop them both into the appropriate size playerpics folder and when Harrelson is traded in late April, change his Boston photo to 15383B.jpg and his Cleveland photo to 15383.jpg.