Vowels in Sign Language

I recorded some videos more to my mastering qualify (the alphabet in Libras - Brazilian Sign Language).

I'm having problems with the Scilab (it doesn't read the videos), thus I used the mplayer to extract the frames. For extract frames from a video, I use the command:

>> mplayer -vo jpeg name_of_the_file.avi

Now, I'm doing tests about skin segmentation. I tried threshold and clustering algorithms, but nothing works with all pictures that I have.
If anyone can helps me, I will be very grateful.

These are some pictures that I have:

Letter 'A':

Letter 'E':

Letter 'I':

Letter 'O':

Letter 'U':