MediaViewer displays images with associated metadata on top of wiki pages. Most of the metadata comes from the extmetadata property of the imageinfo MediaWiki API. 

A credit line is displayed at the bottom of each image, which is currently the combination of the API fields Artist and Credit. If the API result has an Attribution field, that should be displayed instead and the other two should be ignored.

API results are retrieved and processed by the mmv.provider.ImageInfo module in MediaViewer. Credit line display is done in two places: mmv.ui.MetadataPanel handles displaying the credit line at the bottom of the image, and mmv.EmbedFileFormatter generates a credit line for the embed text that's provides when someone wants to share or download the file. Attribution should override Artist and Credit in both places.

This is T67445 in Wikimedia's issue tracker.

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