Is there a limit to the number of images that can be included in an image picker group?

The limit to the number of images that can be included in an image picker group is roughly 250 images.  However, from a practical standpoint, if a user can't find the image they want within the first 50 or so images, then they are probably going to give up.  If you have a large number of images, you would probably want to switch to an external asset management system.  Please see this article for more information about using an asset management system.