Where I can find background photos for quotes

I made website for picture quotes, now I need beautiful photos for backgrounds, where can I find those?

Go to google and type

royalty free background photos

then you will see sites such as pexels, pixabay, unsplash etc

Go to the site select your picture, download and use as you wish.

Safest bet is to type ˝Public domain images˝ - authors of public domain images gave up all rights, so you can be sure you wouldn't have any legal trouble using those images.
Those websites Gringo Monkey mentioned are all very good, I most often use Pixabay.
For editing images - Pixlr.
For adding text and design - Canva.