It's done using a cold mount adhesive that's made for the purpose by
companies such as Mactac and Seal. The adhesive coated sheet is applied to
the front of the print and then that's applied to the back of the plastic
which, in effect, makes the plastic into a thick laminate.

The process is far from fool-proof (ask me how I know!), even for a
professional with the best equipment. Funny things can happen involving
trapped dust and defective plastic and even flying insects getting trapped
while laminating. This is a one shot deal because the adhesive is not
repositionable. There's a high failure rate and the cost of having it done
reflects this. Unless you want to do this on a regular basis and are willing
to go through the learning curve and purchase the required cold laminating
press from a place like GBC, leave it to the pros.

john
tech photo & imaging