In reply to Danny Brown.

Just curious, what sort of tools were you using to find the images? If you were Hotlinking to any images on someone else's server, that's more likely to be problematic for the image not found issue regardless of license, since a lot of site hosts don't like to encourage that sort of thing.

If you were downloading images and putting them into your own media library that doesn't erase the risk of a copyright owner changing their mind about CC licenses, but I usually note where I found it and the date and don't worry about it as much if I was honoring the license correctly when I got it. Have to do that if you're using images for featured images or social thumbnails, anyway, since you can't get the right crops or thumbnails if they aren't processed through the media library.

Using images from Flickr Commons or other public domain sources like the ones you've mentioned also helps, much less likely to have issues that way.