After seeing some cool ideas about displaying the Lego minifigures in picture frames, we decide to do the same for ours. Here is the procedures that we use:
We used IKEA RIBBA picture frame, white. We also got some white mats from the Michael's.
I built a jig (of course, with Lego blocks) for easy repetitive and consistent process.

After some calculation, we decide to place 6 rows, and for each row, we place 9 minifigures. Each minifigure will stand on a 2x4 block. We use width-2 blocks as spacers.

Here is a close-up. In this picture you can see I also build some (4 total) 6x6 blocks as spacers between rows. Be careful not to put too much super glue to the block, as the excessive glue will potentially glue the jig to the mat too.

Each 2x4 block is super-glued to the mat. After one row is completed, move on to the next one.

A better picture of 6x6 spacers in use.

More than half way done.

Little helper working hard :)

Now put the minifigures on the 2x4 blocks:

Final product:
