Before this commit, every images were reprocessed all of the time.
Because the address book may be re-compressed when new pictures are
added, we want to process them and not reprocess the previous ones.
This commit include a size detection so images below the size limit
are not processed.
It's still too simplistic, but the following items have to be here:
- specifying the vCard version supported ;
- specifying the requirements ;
- links to the specifications and useful stuff.
