I can only tell you how I do this in Australia. The best source is family members. Once you've tracked down your cousins, ask them if they have photos you can use. Also, look up archives of newspapers and magazines such as trove.nla.gov.au. It's surprising who pops up. Even a Google search with your relative's name and an interest of theirs, or an employer or something they were associated with will sometimes produce photos. After you've entered your search terms, click on "Images" and scroll through those.
Last night I found a photo of a distant cousin by entering her name and a radio station she used to work for in Google. Turned out the radio station was run by the Theosophical Society and she was a member of the Society. There was a photo of her with one of their leading lights! I also discovered she had met and interviewed Krishnamurti.
