All photos have a copyright. So you either ask permission or your find Stock Photos. Some are free some you have to pay to use.
But you can't just take a credit. When you embed a youtube video that's different because they get more view and paid for them in some cases.
But copying and pasting peoples content is different.
I personally haven't seen that done. Well, maybe once, I saw one poster jump on another poster for content, but I didn't investigate it.
I do get the issues involved. A lot of struggling artists out there.