I don't know how other people do it, but I use photoshop to stitch the pictures together and then upload them as a single file. That is to say, the joining is done before you upload, not after. If you use photoshop you can also do all kinds of fancy stuff like changing backgrounds and so on, but I daresay any graphics/photo editing software would do the job. This tutorial (which is in no way mine, I just found it very handy) has a lot of good stuff about using photoshop to make your minis look good. http://www.platoonbritannica.org.uk/forum/showthread.php?p=21311#post21311