I hope you are not mistaking those "big archives
with lots of cels" with dealers galleries....
Dealers ussually have lots of cels for sale and
they have pics of the cels to show what they are
selling, but they actually own the cels they are
selling so there's nothing wrong with that.....

And if it's not that then, well, i don't spend all
the day browsing for anime cel sites, but i have
never seen any with cels images that don't belong
to them (except sometimes someone ripping of other
pages ad similar). If they exist they are so small
that can barely be noticed or can be mistaken with
a real cel gallery.... You see, we are not
policemen here.... 

You see, what is wrong is wrong, and just because
someone else is doing the same you do without
being noticed doesn't mean that you are doing the
right thing.

Also think that just waiting for the owner of the
cel to contact you to remove the image is not
enough... For example, i own my own cel gallery
but i cannot spend the day browsing the net to see
if someone has stolen the images that i own, so if
so is someone goes and makes an archive including
the images of my cels i probably don't become
aware of this unless someone sends me an e-mail,
but chances of that to happen are almost none.