Here are some useful image tools on the web. It's not exhaustive and there are better fee paying programmes available, but for free, these arent bad at all. There are some tools here that are used for as masking tech- I have included them for the reason that if you know they exists and how they work, you will spot and recognise them if you come across them in your work.
There are 3 main types of image searches to carry out when looking at an image
1. Looking for like or similar images
Using Google images will search for like or similar things in its data base. Upload the image to Google and see what returns. Most searches still require a visual check to find the same or similar, but it is very effective.
Do not upload sensitive images onto the site. You are effectively sending the image to google. De sensitise it or crop.
2. Look for the same image on the internet.
Tineye will look for the same image ( or at least 80% same ) so your results are the same image elsewhere on the web or the original it was taken from should there be 70-80% remaining of the original image. Do not upload sensitive images onto the site. You are effectively sending the image to tineye. De sensitise it or crop.
TinEye Reverse Image Search
3. Exif Data