To answer your question, I say not to use the image/cover outside of Webnovel because the images and fonts that I use are for non-commercial use. This means that the creator/artist is okay with them being used as long as no profit is gained by publishing them and not claiming their work as your own. Since majority of Webnovel’s original-novel authors are posting their book for free, it’s not violating the non-commercial use condition that they have.
Now if someone did want a cover outside of wattpad (like Amazon for example), I’d most likely have to either use royalty free images (100% free, commercial and non-commercial use allowed) or buy stock. Or even create something myself. This also applies to fonts. I’d either use free fonts, or buy a license for the font to be used. So that it wouldn’t violate anything and wouldn’t get the author/graphic designer in legal trouble. Also, these covers are usually not free, because once again, I’d have to buy stocks and fonts, not use free resources. Usually, they’d cost about 20-30 USD (depending on the time and resources used) for a standard license, that allows for 500K copies to be sold. For this type of cover, the author would have to PM me on discord or email to get exactly what the author wants.
