pamdice splits an image up into smaller ones.
pnmtile concatenates a single input image to itself repeatedly.
If the anymaps are not all the same height (left-right) or width (top-bottom), the smaller ones have to be justified with the largest. By default, they get centered, but you can specify one side or the other with one of the -j* flags. So, -topbottom -jleft would stack the anymaps on top of each other, flush with the left edge.
The -white and -black flags specify what color to use to fill in the extra space when doing this justification. If neither is specified, the program makes a guess.
All flags can be abbreviated to their shortest unique prefix.