Your book cover images are trash and I don’t blame you. There isn’t a good compendium of high-quality cover images and metadata for books that you can use for commercial purposes. Google books is amazing but they won’t let you use it for commercial purposes so there is a huge hole in the market if someone is willing to solve it. Calibre does a pretty good job, but it has its own algorithm that is very convoluted and involves searching Google images and multiple other sources and compiling them.