Here is the legal policy that DMB is using regarding player photos.

"Imagine Sports, Inc. (“Imagine Sports” or the “Company”) is pleased to provide a new feature that allows you to upload any image to represent a player in the game. Due to copyright and trademark laws, the Company cannot provide pictures that contain player images or team logos or other copyrighted images, nor can Imagine Sports direct you to any repositories or databases of player images that may exist. You may upload any picture or image to represent or symbolize a player, and any such use may be allowable under “Fair Use” and other legal concepts of non-commercial use. However, Imagine Sports is not responsible if your use of any image constitutes a violation of trademark or copyright laws of the United States of America or any other nation or jurisdiction, and you assume the risk of any such use. 

Diamond Mind Baseball is a product, copyright and trademark of Imagine Sports, Inc." 

The game has a mechanism to upload zipped files of photos. Where they come from is up to each user to determine.