Realistically anything you publicly publish that cannot be copyrighted can be used by others. Within a community of hobbyists, the courteous thing to do is to ask permission of the person who scanned or photographed the image.

I distinguish between linking to an existing scan, and making a copy of the scan for another server. Again, it's not illegal to link, but certainly shows disrespect to the owner to use his scan on his server. Often, it represents added cost to him if he pays of bandwith to his server.

Showing an image in an online auction that doesn't represent the item being sold is another matter. Often, it doesn't matter (in the case of unused chips, for example). Sometimes it matters a lot, and I agree with the other poster that if your chip is not perfect, you should state that the image you use is not of the item being sold. Some use the term "file photo" or "representative scan".