Do you mean sending images from a site to imcdb?
Buses on screen is SteveA's site, so a comment + link to indicate that the pic comes from there is enough. Same for other sites to which was already already had contacts and pictures uploaded. But for all other sites, it is always better to ask first to the site owner.

Or do you mean sending images from imcdb to a site?
Then if these images were captured by you, you do what you want with these. For others, we usually ask to the other site to mention somewhere that the images come from imcdb. As we do not have the rights on these images we cannot forbid others to reuse them anyway.