Free-/Open-Source-licensed JPG, JPG-XL, PNG, TIFF, PDF, PostScript files for print filter and OCR CI testing

Hi,

recently, we added several testing facilities to OpenPrinting, but some of them, 
especially those to test software to handle data which gets printed or which got 
scanned, need sample files which can be shipped as a part of the source packages 
of the component which includes its tests.

For this we need files of the formats JPG, JPG-XL, PNG, TIFF, PDF, PostScript, 
and perhaps even Apple/PWG/CUPS Raster which are published under free licenses 
so that we can include them. Ideally the files also come with different 
properties, like grayscale, color, 8-, 16-bit, different resolutions, page 
sizes, number of pages, ...

We appreciate a lot if somebody could suggest us suitable sources.

Note that the PWG source

https://ftp.pwg.org/pub/pwg/ipp/examples/

is not suitable, unfortunately, as there is no license. The README files only 
mention the copyright holder but no license for them (my suggestionis that PWG 
publishes sample files under free license).

Thanks in advance for any suggestion.

    Till