Fafi, you go into a small room with 3 or 4 other girls and are given a gown to wear, you take off your clothes in that room and then come out and put your chest against the Xray. They dont watch you get undressed or anything, and its only very quick for the Xray. Its a female doing the Xrays too, so dont stress! I was worried because i had a small tattoo that sits just under my underpants (that I hadnt told them about) but noone was there to see it, so it was okay. If you had a tattoo anywhere else though they would see it, so its a good idea to declare it =)
One of my friends had a nipple peircing in for the first Xray.. the poor technicial had to pull her back in and ask her what it was