I have often illustrated my blog posts with my own photos. However, recently, I have been using a lot of AI-generated images, and occasional photos from websites that offer free photos.
I have just come across an excellent source of illustrations, from the Public Domain Image Archive, a collection of thousands of out-of-copyright images curated by The Public Domain Review.
The searchable archive includes background information about each image. The service is free, but the project relies on financial support from donations and sales of prints.