If you have ever meandered your way through an internet search for images I'm sure you've come across images from stock sites that look like this one -

Stock sites usually overlay a large watermark on their images to prevent use. They want to make certain people are buying the images so the artists get compensated for their work.

I've seen designers yank one of these images off the internet and use it to make a cover. It  looks tacky and makes you seem as if you have no clue what you're doing, these images are very often low quality. Again, to deter people from using them without buying them. So you'll likely end up with a blurry image that has the stock site's name splashed across it. I don't know about you, but that isn't the cover I want representing my work. 

This is the purchased version of the image. The original size is 8510 X 5674 at 300 dpi. I had to make it smaller to upload it to Wattpad because it was a 10mb file and wouldn't up load. The watermarked image that I swiped from the site is 1600 x 1167 and only 72 dpi and the file size was 460K. There's an obvious difference in quality between the two files.

You may not see it here, but if you PNG the couple, the image becomes even smaller because you've eliminated the background. When you put that PNG on the canvas for a cover you'll have to size it for the cover and if you make a low resolution image bigger it will become fuzzy. 

This is the cover I made with the purchased image 

This is the same cover with the stolen stock image

It appears much less professional, and while in this case the image didn't become overly fuzzy, it's not grand.

It's very hard to find the right image at times and you're very tempted to use 'that perfect picture' even if it does have a watermark on it. There are a couple of instances where you can get away with using a watermarked image. If you've ever seen the images from Getty, you know their watermark is quite small and doesn't cover the entire image. Their images are often high quality as well. 

The watermark on this image is low enough that you could still use it for a cover, just put the watermark below the edge of the cover. I'm not encouraging stealing here folks, but for Wattpad covers we tend to slip a toe over the line of 'hey that's not right' sometimes because many covers do feature celebrities as face claims. You would NEVER EVER do this for a published book. It would open you up to a lot of law suits from various people and companies. 

Be choosy with the images you end up using on your covers. I've rejected requests because I simply couldn't find the image that fit their request. I'd rather pass on it than make something I'm not proud of or the requester will end up hating. I do my best to create professional work. I treat every request as if it's going to be used professionally. Slapping things together 'just because it's Wattpad' isn't how I do things. If that's your attitude then why design? Everything should be treated as if it's important, every single request. These are essentially your clients and they deserve the best work you can produce. They aren't any less important just because it's a Wattpad cover. 

If you want to represent yourself as a designer then act like one and make the best graphics you can. If you're just here to slap things together then you're not a real designer and you have no intention of improving. Don't treat it as this thing you do just cause you're board, if it's what you want to do, even if it's a hobby and you have no intention of moving into the professional field, do your best work and represent yourself professionally. Let your work speak for you. Let people see the beauty you can produce.