The program to me seems to pick a few tiles most fitting for each color and use the same over and over...doesnt seem too concerned with variation. if we're using this program I think it'd be good to divide the big picture in different sections, then assign a set of tiles for each section...that way we assure all the tiles get displayed.
Well, in a picture that big you have over 10,000 tiles. That said, it means that every unique tile is used 26 times, if they are evenly divided. But of course they are not. But still at least there's a possibility that all of them are there, some more than 26 times, some less. To be sure, everyone should try to find all their tiles at least once and then report back to us if they didn't find all of them.
At least I found all my tiles.