Created attachment 84866 [details]
example document showing the described effect

If you insert an image from a file that does not contain information about the resolution (in DPI) -- e. g. a GIF image -- then Impress uses a default value of 96 DPI multiplied with the scaling of the user interface (i. e. the Windows desktop scaling multiplied with the UI scaling configured in Open Office). When you now crop a part of this image the cropped size is stored in cm (or inches), not in a relative portion of the entire picture. That means if you now change the either the Windows DPI setting or the UI scaling of Open Office (Options menu -> User Interface -> scaling) the cropped part of the image changes!!!

To reproduce this effect take the attached example file and open it with different DPI settings of your desktop -- or with a Open Office UI scaling different to 100% (Options menu -> User Interface -> scaling). In this case the graphic on the first page (GIF image) will change but the same graphic on the second page (imported TIF with built-in DPI value) keeps unchanged.

I think this is a bug because the look of a document shall neither depend on the Windows desktop DPI nor on the user interface scaling of Open Office. Imported images without a given resolution in DPI should be treated with a fixed DPI value independend from Windows and OO user interface scaling.