Images can't be add to measures or remains sticked in frames
OS: Windows 10 (10.0), Arch.: x86_64, MuseScore version (64-bit): 3.0.0, revision: 6e24695
1) Create an image eg (attachment)
2) Drag and drop this image onto a measure/rest/note
Result: nothing. The image is lost.
3) Drag and drop this image eg in the Title vertical frame
Result: the image is imported, and can be edited. But you cannot move it, remaining sticked at the same place.