If you're looking for an image on the internet, it's pretty easy. But there are also some systems available which offer what's known as a reverse image search. Upload a picture, and the system will give you details of any web site which currently contains a copy of that image. If you want to check whether any sites have misappropriated a picture you previously uploaded, and are perhaps abusing your generosity, then a reverse image search will tell you.
Also, if you receive a suspicious email message which you fear could be a scam, performing a reverse image search on one or more of the pictures contained in the message can be a helpful tool in trying to verify the legitimacy of the message you received.
TinEye is an excellent reverse image search tool, which you use simply by uploading an image from your PC. Or you can specify the URL of the image, or drag it straight from your desktop. There's even a downloadable add-in for Chrome if that's all too much bother. TinEye claims to have a database of some 15 billion images on file, and is free to use.
Link to Tiny Eye Website
[Courtesy of Gizmo's Freeware]