How to retrieve image files embedded in a presentation?

How can I retrieve the image files that were embedded in a presentation? Someone created a presentation and embedded image files in it by dragging and dropping them on the presentation. How can I retrieve these image files as independent files that are separate from the presentation?

If the presentation is saved in odf-formatted files, this are zip-Archives. So the direct route would be to open the file as a zip-Archive and extract the pictures.
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Impossible for encrypted files…
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If the presentation was saved as pdf, there are specialized tools to edit pdfs. Using Draw may be a bit tedious…