If one imports a photo to Inkscape, he can get a drop shadow by selecting Filters > Shadows and Glows > Drop shadow. If the photo is scaled or rotated, it still works.
Surprisingly, if the photo was cropped by adding a vector element as a clip path (Object > Clip > Set), the drop shadow filter does not work, because the clipping happens also to the shadow.
Fortunately the clipping can be released (Object > Clip > Release). After that one can duplicate (=ctrl+D) the vector element. Now there are two vector elements. One of them can be used again as the clipping path of the photo. Another can be colored (=grey fill, no stroke) and be used as the drop shadow (Object > Lower to bottom + move a little).
If a blurred shadow is needed, it's easiest to go Filter > Shadows ang Glows > Drop Shadow.
Addendum: The story above concentrates to making shadows due the comments. Of course the extracted clipping path is available for other purposes, too