I'm not sure if it would be safe to assume that most users of Moodle are academic institutions (universities, colleges, etc.) but it seems a safe bet that if the above is true then they have a method for creating picture ID cards already in place. Knowing that, it's quite likely that these institutions already have a database or file repository with the pictures stored in a format that the institution has decided upon and with an institutional naming convention.
It would make sense then to have a module or component of Moodle which would simply look to this location for an image file rather than upload the file to yet another location. Sort of like your current use of Gravatar (without the Gravatar restriction).
I realize that in the grand scheme of things this is a really minor issue but I did have a system in place for 1.9x that worked fairly well. I can no longer use that system in 2.x because the way Moodle stores files and locates them has changed drastically. I have faculty (and some admin) that are adamant that the picture (avatar) of students MATCH the picture on their photo ID.
The bulk photo upload doesn't seem to work for me and even if it did it would only work AFTER students log in for the first time.