In another well known spreadsheet progragmme, dragging-and-dropping a .jpg file from the file explorer to the spreadsheet inserts a graphic into the spreadsheet at the currently selected cell.
In Calc, dragging and dropping a .jpg makes LibreOffice open a draw document and inserts the picture in that.
Images can be succesfully inserted in a sheet from the clipboard, or by using inssert-image-from_file, but not by dragging and dropping.
already known issue.
*** This bug has been marked as a duplicate of bug 61233 ***