Over the years, I've done a lot of book covers (200+ at last count). I enjoy doing them (usually) because they have a lifetime far longer than advertising are commercial brochures. I occasionally find covers I did 30 years ago in second-hand shops... and have to buy them to prevent anybody else seeing them. As an avid reader, the first real notice I took of commercial illustration and design was through book covers (still a big fan of Chris Foss, Jim Burns and Bruce Pennington.) I still think it's cool that I get to do it as a job!
Some design themselves, others are hard work because there's nothing visual about the MS, or it's a subject you don't want to show explicitly (like gender reassignment.) Some are a challenge because the author insists on using something specific (in one case, a happy snap of their cat...). Although I've worked on a number of picture books, I've only included a few here because the illustrator usually has a clear idea of what the cover should be, and my job is simply to make it production-ready. The ones I have included entailed major work beyond placing their illustration on the page. In these cases, I like to discuss it directly with the illustrator as it's their book - not a chance for me to show off. Anything I do has to help make their work shine, not take it over.
The various elements for these covers come from a wide variety of sources - I have attempted to give credit where due.