Ever wonder how the thumbnails when you hover on the progress bar for YouTube™ videos? Turns out the process is not that difficult. In fact, you can replicate the process for Free.99. Here’s how. Before We Start Download and install Image Magick, if you don’t have it already. Follow the steps in the DIY on thumbnails to generate your images. Let’s Get Started! Convert the JPG files Using the thumbnails generated during the DIY on thumbnails, generate a strip (or sprites) of the joined thumbnails.