I often have wondered if posting my images on facebook, google+, twitter, m blog, etc is safe. I do always watermark my images and put a copy write notice but, you never know......or can you find out? I'm going to show you how to have a check to see if anyone is using your images. The common term for this type of search is called "reverse image search" I did this in firefox, but I believe the process is very similar in other search engines, the wording might be a bit different, but if you can learn to use a dslr you can learn to do this!
The first thing I must however tell you is, if you have a dslr camera, you should be able to put specific info into the metadata,(if you don't know how, do a search with the make of your camera ) Well when you do this make sure you put your name in and phone number. Then in the case of ownership deputes you info is always there.
The first step is to find your image on your site and right click. A pop up box will appear click "copy image location"
Take this copied number and paste it in your google search bar. Click search!
The next page will look like this on, click on where it says "search by image"
The next page will show you hopefully that your image isn't being used anywhere else, or will show you where people are using your images, even if they have cropped the image or altered it, like removed the watermark.