Images are a crucial part of research. The sites below will help you to find where an image came from as well as see other images that are similar.
Basic
Google Images - This facet of Google allows users to search by image, either by finding one online or uploading one (click on the camera to upload an image).
TinEye Reverse Image Search - Similar to Google Image Search, TinEye allows users to search by image.
9 Tools for Image Analysis - From Arizona State University's News Co/Lab, this site compiles a list of websites that provide tools for both basic and advanced image and video analysis.
Advanced
Tracking the Source of Viral Photos - This chapter in the book Web Literacy for Student Fact Checkers walks through how to research viral images and figure out where they came from.
Using Google Reverse Image Search - From the same book as above, this in-depth discussion guides readers through the process of finding out if an image represents reality, including questions to ask and steps to take to investigate.
These links provide information on the history of image manipulation, tracking edits to an image, and how to discern if an image is unaltered.
Faking It: Manipulated Photography Before Photoshop - Although Photoshop makes it easy to alter photos, image alteration has a long history, extending back to the dawn of photography. This exhibit from the Metropolitan Museum of Art delves into all aspects of image alteration.
The Hidden Signs That Can Reveal a Fake Photo - This BBC article outlines ways of assessing an image to see if elements are faked, including looking at reflections, shadows, and more.
Snopes: Fauxtography - While Snopes is best known for fact checking textual information, it also investigates photographs, distinguishing between real, fake, and real images with fake backstories.
Real or Photoshop - This engaging quiz from Adobe tests viewers' knowledge of how images are faked by presenting images, some real and some fake, and asking the user to determine which are real.