This is a fun thing for Christmas. What do you do with all those digital pictures? I've got mine backed up on a lot of disks, and they never see the light of day. So, with the daughter finally ending her water polo career, I was going to make a big poster with her history of sports.
I used an old program called Fotowall, which is on the standard distribution, but hasn't been touched for a year. It works well, and will throw your pictures on the mat, which you choose. The nice thing is that it is totally compatible with Inkscape, so you make an svg, and finish it on Inkscape.
Then I export it as a high-res png which I then process with Gimp. That's just to do a final cropping trim, since Inkscape leaves ragged edges. I'm going to use something like 18 mpixs for the final jpg, which I will take somewhere. Posterjack is good, but I'll probably use the local Costco.
Here is a sample, highly reduced to stop porn-revenge sites. :)