Well, to be completely honest my reason is that 
I'm extrememly possesive.  That cel is _mine_,  
and if someone wants to use the image I'm fine 
with it as long as they ask me first.  I feel 
that it's common curtesy to do so.  

I have a friend with a rather nice cel posted on 
her little known page... and then all of a sudden 
she sees it as the image for a webring (and no, 
the image wasn't a screen cap)!  For her the 
worst part was that people thought that the cel 
belonged to the girl who started the ring.  My 
friend is very proud of owning that cel, and it 
was very rude on the part of the webring owner to 
use the image without her permission.

I really think that it all comes down to being 
polite.  If you don't care about others using 
your images, then thats fine.  In fact, I envy 
you  ^_^  But it would be nice if people could 
respect others wishes a bit more...

Best Wishes,
Jenny