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openendedsky it was actually super easy. they were amused (although I think also confused) when we brought it in at the gate. the key was that our board was foldable. so getting it on, say, Everest, was as easy as folding it in half (being careful not to dislodge any glued-down pieces) and stowing it in the pouch in the front of the seat. Of course I knew when the on-ride photo was coming, so we just made sure to pull it out a little while before then.
Just a note, the staff at the everest gift shop loved the photo so much they kept it on display first at the photo desk and then on top of the monitors for viewing photos for over a year! quite an honor. this was definitely something i got to cross off my WDW bucket list.