People often overlook the importance of filenames when it comes to improving the SEO of their website and their WordPress themes. There are two simple things that everyone should be doing.
1. Make filenames machine & human readable
No one is going to be searching for IMG-938398734.jpg, but they might be searching for pictures of cats playing with yarn and could come across your website if your file was named cat-playing-with-yarn.jpg. Having clear descriptive filenames is one of the easiest ways to improve your search visibility.
2. Utilize alternate text
Before inserting your image, be sure to fill out the alternate text field. It is arguably the most important factor that affects the SEO of your images. For more specifics on how to best use the alt attribute, check out this article.