Several ways: At first, years ago, enough publications or authors asked me to confirm permission to use the image that I realized it was popular. Some of the publications attribute the image to me. The MRI image itself (https://www.flickr.com/photos/lizhenry/2051224366) has my name on it. And, finally, a reverse image search, these days shows hundreds of thousands of uses. I always wanted to use my brain in the service of science and literature, but didn't know this is how it would happen! ;)