Do you plan to set up a current MLB league? If so, I would recommend Bigrod's hi-res photos:
http://www.ootpdevelopments.com/boar...-released.html
Place the extracted files into the "photos" folder. Then proceed with setting up your 2012 MLB league.
NOTE: You can also download and install the all-in-one mod (available through Add-On Central). There is a link to Add-On Central at the bottom of the main OOTP13 startup screen. Install these add-ons before you set up the 2012 MLB league.
Here's a screenshot featuring a hi-res photo: