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I'm using pixabay.com when I'm not using my own photos. There are similar services, like Pexels. It's a good habit to mention that images are from the sites if you're using those :)

Imgur.com was on my radar for while also.

Images on imgur might not be free for commercial use, as images on Imgur might be violating copyrights themselves.

This is a special world when we're making money on the site, so we actually need to think what we're doing :)

Himm, I will check your sources maybe fits better for my need without any copyright problem. thanks for the help.