Well, I hope I don't confuse anybody with the title of the topic (and with my english), but i didn't know how to express my doubt.
The thing is that I a school teacher and I trying to design a little course of inkscape for my pupils, and in the final part i want to put them an exam, in wich they have, for example, to reproduce some images that i give them. I would like to know if there is any way of blocking those images so they can't just copy and paste instead of doing the whole process. I have worked in layers and i've blocked the one which I don't want them to use, but they could easily unblock them and cheat me...
This is the exam i want to put them: http://www.mediafire.com/?1tywpyeixyc
Thanks a lot.

How about replacing the target images with a raster version? (Edit->Make Bitmap Copy) and deleting the vector to the file handed out?

-Rob A>

Ups!! you made it simple!!
Thanks a lot.
Tucho Mendez