Click on the + sign next to the search box for the Advanced Search options. Type "photograph" in the Medium field to limit to photographs.
“Portrait of 78-year old rajasthani woman wearing headscarf, Gagadi (aka. Gagari) village, Rajasthan, Indian,” photograph, n.d., Bridgeman Images POV1077168, copyright Chinch Gryniewicz, web.
Use the Google Images search feature to find a matching or similar image.
Drag your mystery image into any Google search bar that contains the camera icon, or click on the camera icon and paste in a url.
Tineye is another excellent reverse image search.
"How to Identify Mysterious Images Online" by Tasha Bergson-Michelson gives step-by-step instructions.
Use this search to locate images that are licensed for sharing.
These search engines are designed specifically for image searching.