Many times have I come across an image with no source given, and no signature visible, or someone else is asking where a particular image comes from. I’m writing this in the hopes that next time you post an image you found without a source, you spend the 5 minutes it takes to at least look to see where it came from.
There’s three main sources I use for image searches.
Going to https://images.google.com/ and clicking on the camera icon on the right of the search bar will bring up a “Search by image” popup where you can upload an image or feed a URL to search by.
Once something is uploaded, you’ll be given the option to “Find other sizes of this image”. Click “All Sizes”, and you’ll be shown all images that are similar to the input image.
Tineye is a bit easier to use, just go to https://tineye.com/ and upload your image. Tineye lets you search by age or size, which helps find the original source of the image.
Bing images is similar to google, go to https://www.bing.com/visualsearch and upload your image.
One advantage here is that you can crop the image (Click “Visual Search” at the bottom of the image) to cut out bits you don’t want to be looked at.
Finally, you might need to find a somewhat larger image with one tool, then use a different tool to find the full original. Keep trying different tools until you either find it, or give up.