For U.S. based photographers, registering your images with the US Copyright Office will put you in the best possible position to claim any damages for any illegal use of your images. Submitting images in this way will register your claim to their copyright and then record your claim to its public database.
One thing that is a pain about this process is filling out the excel spreadsheet to submit to the copyright office with the names and dates of the photos to be registered. Photographer Andrew Keithly has found a way to use a tweaked Excel macro to ease the pain of copy and pasting every single data point one by one.
Here’s the video tutorial:
Andrew also has a great blog post that goes over the process in detail: https://www.studioagk.com/post/image-copyright-registration-tips