Correct me if I am wrong, I vaguely remember that one of the wonderful features of Discourse is that if someone posts an external URL image link in his post, the image will not only appear in the post, but a copy of the image will also get saved on my server.
Is this true? And how do I verify that copies of these external url images are being saved on my server? Where do I go on my server to locate these images?
Search for “images” in your settings (/admin/site_settings/category/all_results?filter=images), there are any image-related settings, including the one that downloads copies. It saves them where you normally store files when a user would upload them.