Board Thread:Questions and Answers/@comment-29058994-20160716164928/@comment-6697950-20160717071955

It's not mandatory for uploading an image, but it is mandatory for adding the image to an article. It's to ensure that those who upload images properly source them, so that other people wouldn't be stuck having to do that for them. It's a very common problem with new people who start uploading images without reading the guidelines first.

Only the very original source is considered to be "the source". If you find an anime or in-game screenshot on some website, the anime/game is still regarded as "the source", though in case of obtaining a screenshot from a third party source, we usually indicate it as a note. For example, "Source: Episode 1. Screenshot taken from [site]." Though, only the original source is mandatory; the note is just for clarity and crediting purposes.

As for providing a link, just copy-paste the URL of the site that you found the image on. Though, this is mostly used for posters and character designs taken from Dengekionline, swordart-online.net etc.