Here's another vote for magnets and steel sheet. The easel you show might be great for deliberate distortions but heavy paper might just be too much trouble to keep flat and if you need to distort a photograph, you can most likely come up with something just as versatile.
When I made my magnetic easel set-up, I used really strong ¼" (6mm) rare-earth magnets, which I embedded into hardwood strips that were planed true and painted flat black. They're easier to lift and position for me and I've yet to meet the photo paper that can't be held firmly in place with these, though my prints are rarely as large as 16x20". You could even go so far as to embed some of these into your baseboard to hold your sheet of metal in place as a semi-permanent easel.
Eli
