Some graphic resources (both free and paid) for designing book covers, logos, flyers, certificates, brochures, and more.
Website with thousands of images. In the search, you can select what you want to search for and choose the "free" option.
Also good.Free PSD VN (free PSD flyers, text styles and actions for Photoshop)
PSD Keys (identical website)
On this very popular site, you can create 3D titles in large format with a variety of effects and fonts and save them as PNGs with transparent backgrounds, for free.
Cut out pro
In the free version, you can improve and resize a photo with A.I. (artificial intelligence). The result is wonderful, it corrects pixel by pixel.
There is a paid option, but in the free version, you can download one image per day, without registering on the site (I've already tested it).
Generates thumbnails and Screenshots of your website.
Photopea (great alternative to Photoshop, it's online and totally free! Edit PSD, EPS, AI files, and more)
Paid options:
This site, from the Envato group, has thousands of images at affordable prices (from $5). You can buy editable flyers in PSD or EPS, which you can use for the cover of an eBook or poster, t-shirt designs, logos, and more.
Elegant Flyer (great quality flyers at affordable price, starting as $ 3,90).
Easily remove backgrounds from images.
In the free version, with registration, you can download an image.
After that, you can purchase credits starting at five dollars.