Someone shares a dramatic photo with a confident caption. You’ve got about a minute before you’d normally either believe it or scroll on. Use that minute for a reverse image search.
Upload the image, or paste its address, into a tool like Google Lens, TinEye or Bing Visual Search. They return pages where the same picture, or a close match, has appeared. Sort by date if the tool lets you. The oldest result is often the real source.
What you’re looking for
The most common problem is a real image with the wrong caption. A photo from a flood in one country gets shared as a flood in another. A picture from an old protest gets recycled for a new one.
If the earliest appearance predates the event it supposedly shows, you’re done.
When the search comes up empty
Crop the image and search again on just the interesting part. Look for signs, license plates, shop names, landmarks. Then check shadows and weather against the claimed date and place.
No result doesn’t mean the image is fake, and one result doesn’t make it true. It’s a first step. But it’s a fast one, and it catches most of the lazy stuff.