permission forbidden

I get to teach my first art lesson this coming Tuesday to a group of fifth graders. I was all excited about my lesson/nervous until I found out part of it's not going to work. My lesson was on Andy Warhol (of course), and I was going to have them sort of re-create his picture of Marilyn Monroe. I was going to take a picture of each student, have them draw the details of their face (lips, eyes, etc.) onto a transparency sheet, and then paint blocks of color on the actual picture. The finished product would have the detailed transparency placed over their painted picture to simulate the Monroe piece since it's not easy to do the whole screen printing deal. I found out today that I have to have their parents' permission to take their picture, something that will not happen in the alloted amount of time. I didn't even think about that nor did my teacher (obviously or I would have changed it already). It saddens me that there has to be so many restrictions and protection on students these days. If only I had been born in the '70s or earlier...