@Keet
I really don't understand why you would search the internet for a cover picture to fit your book. Nowadays it's so easy to take a picture with your phone. You would have to use a photo editor anyway to make it fit so why not take a picture that truly represents your book? If you don't like it you just take another photo and try again. No worries about copyright because you will own the copyright.
As someone's who's designed his own covers for years, there are still issues. I 'created' my own images to precisely fit my books, patching various images together, but these are incredibly difficult to pull off, even when you know wtf you're doing.
What's more, if you use anyone (besides yourself) as a model, you'll need to download a photographer's 'rights allowance' document and get it signed (trust me, an ex is likely to 'change their mind' once they're no longer an active girlfriend).
But, at least in my case, my personally crafted images were rarely as successful as the stock images I purchase (though a subscription service, where they only cost $4 per image). The image is that the lighting varies for each image you combine, and it's incredibly difficult to overcome those lighting/shading issues.
The key, emphasized repeatedly by designers, is that book covers are NOT literal representations of what's in the book (since professional designers rarely read the books they're hired to provide covers for). Instead, covers convey the central themes and impressions. Thus while they won't represent actual events within the book, as long as they convey what the book covers, most readers will accept it.
Again, covers sell books, they're not intended to aid the reading of the book once it's purchased.