Identifying the copyright holder may be straightforward or require some detective work. Take special care if you have found an image that you are interested in via a search engine such as Google Images. They only cache a copy and the thumbnail page does not display any copyright warning. You must go to the original site to see the image in its original context along with any ownership details. Many people have incurred large bills by assuming Google Image thumbnails may be freely used.

Work displayed on most websites will be associated with a user or domain owner who may be approached. Image files themselves will often contain metadata identifying the rights owner and giving contact details, but unfortunately browsers do not support display of this information. There is however an extension for Firefox called EXIFviewer which will display IPTC and EXIF metadata.

If you cannot find the rights owner it is only safe to assume that although the photo is an 'orphan work' it is still someone's copyright and is unsafe to use. Copyright persists for 70 years after the death of the photographer so some very old photos may be OK, but beware that some agencies regard scans as new work so within copyright even though the originals have lapsed.

Note that the copyright holder may not be the publisher, who may be using the image under licence. Equally, sometimes the credited author will not the copyright owner because they have assigned copyright to someone else but retained their moral right to be identified as the author.