Not really rules at all... just common courtesy.  

If someone buys a cel, and puts the time and 
effort into scanning the cel and creating a 
website to showcase that cel .... It is just 
common courtesy to ask that persons permission 
before taking the image from their site.

Personally, I don't care if I see my cel images 
out there occasionally, but other collectors have 
a real problem with it.  And rightfully so.   

so, while 'stealing' images off pages isn't 
really illegal... it's just not a very nice thing 
to do.  If you are going to use someone else's 
cel image, all we really want is for you to ask 
our permission first, and give credit where 
credit is due.

(I use the word 'You' in reference to any image 
stealers who might be reading this.. it's not 
directed at you personally, Kasuga-kun)  ^_^