Created attachment 143973 [details]
Five files, from new empty document, to document with frame and Bitmap removed again.  The filesize has not shrunk.  The image ("Bitmap") file used.

Removing an imported bitmap from a frame does not remove bitmap file from .odt file.


Actions to reproduce:

Add a frame:
Insert | Frame-> | frame...

Add a background to it, in LibreOffice parlour a "bitmap" that must first be "imported", and then added as "Area":
<Select frame> | Properties... | Area | Bitmap | Import

Observations:
* The imported bitmap becomes visible as background to the frame, but is not visible in the Bitmap pictogram list in the Area tab.
* The document grows in size according to the size of the imported image.

Actions to reproduce:

Remove the background:
<Select frame> | Properties... | Area | Bitmap | None

Observations:
* The background disappears.
* The filesize remains the same, even if the Bitmap is not being used anywhere else in the document.
* There is no interface to list or remove the Bitmap.
* The file and reference to it can be found inside the .odt file in a folder ./Pictures and in Styles.xml.


IMO this is a bug, as it lets a Writer file grow without limit and without method to prune it.
* LibreOffice should add imported Bitmaps to the Bitmaps list, or to a more general management GUI for imported data.
* LibreOffice should have an option to manually manage Bitmaps contained in the document, used or not.
* LibreOffice should perhaps automatically remove unused Bitmaps from the document file.