Pictures are property of film companies, yes, but even if the sites do not have copyright on them I do not like to take these pictures without asking because it may take time to collect those pictures (I know it, since I uploaded lots of pictures on IMCDB).
When it is for 1 or 2 pics there is no need to ask to the site, but for taking 10-20 or more pictures I prefer that the site owner is informed before, rather than discover some day that the pictures of his site was copied to another one.
I hope you see what I mean