Cropped images and export to PDF: old problem IMO.
My workaround for only working on LibreOffice is as follows:
- edit (crop) the image in Draw
- in Draw: Cut or copy the image into the clipboard
- in Draw or in Writer ↦ use (menu Edit) Paste Scecial
: Insert the image as a Bitmap: The image will be really cropped and pure.
Using the Paste Special mode can be done these ways …
- via menu Edit
- via shortcut CTRL+SHIFT+V
- via clipboard icon ↦ triangular selector
I have not searched on the bug tracker about this problem. A feature request (add your statement or create a new one) could be helpful.
General advice
Edit images in dedicated programmes like GIMP, IrfanView, XnView etc.