On e.g. help animation files, such as https://commons.wikimedia.org/wiki/File:Wikipedia-ios-3d-touch-shortcuts.gif the element which are not "own work" (by MHurd (WMF) in this example) should be attributed.

For article texts if visable, please use e.g. https://commons.wikimedia.org/wiki/Template:Wikimedia-screenshot.

(paraphrased quote)
"If the screenshot contains any picture hosted in Commons, you should credit them properly (adding the link and author, in the "author" field at the "Information" template, as additional licensing), or elsewhere, avoid its displaying. Notice that if the screenshot contains any non-free picture depicted (such as backgrounds owned by Apple), you shouldn't upload the screenshot/animation to Commons, even if the main subject is the app rather than the screenshot itself ("de minimis" does not apply). If you really need to upload your screenshot with a non-free picture, you must crop out the non-free picture."