Originally Posted by DeanCapture

Emmanuelle, this is going to be a tricky situation. If you can get away from using white background with light skinned people - that of course would be best. If you can't - consider doing this:

Go to the fabric store and pick up some black fabric. Hang the fabric on each side of the girls (as shown in this illustration). Get it as close to the girls as you can without it being in the picture. Place your mainlight directly in front (flat lighting). The black fabric will act as a negative fill light and tone down (darken slightly) the outer edges of the girls skin and that will help to seperate the edges of the girls from the *bright-white* background. This is done a lot in the Glamour/Fashion industry. If you have some time, experiment with not using the fabric and then with using the fabric. You should see a BIG difference.

Good luck!