I just got an email back from Guest Relations in regard to the pictures that I submitted to the Happiest Faces on Earth event :
Confirmation emails and letters will be sent in late-May to all participants confirming receipt of photo and, if the photo is used, notification of the general placement of the photo in the collages. Additionally, when you visit the Resort during the 50th Anniversary Celebration, you may also find information on your photo(s) and its usage by visiting one of three Happiest Faces On Earth kiosks that are located inside Disneyland park.
I guess I just need to find where the kiosks are! I hope this is helpful to other people who are wondering!