Insert an opening pick as far as possible into the seam between the plastic front and the metal rear panel, on the right edge of the iPod.

Use the opening pick to pry up against the plastic front panel and release five retaining tabs (seen in the third photo).

Slide the pick along the edge of the iPod and continue prying to release the rest of the retaining tabs.

After all five tabs along the right side are free, the case should open easily.