>>2105157This is how you do it:
Select the white background wherever it is visible, like in the roughness of the edge or below a smudge of black (shows up as grey).
Maybe grow or feather the selection a bit to make sure you have everything and soften the edge.
Use the "Color to alpha" tool (GIMP) to turn white into transparency. Everywhere that was grey will turn into partly transparent black.
If you included the shadow earlier, delete it in the next step. Else do steps 1-3 for that shade of grey.
Lots of jpg artifacts around the edges, so select all transparency with a high treshold wand. Invert, grow, invert again to keep a little space around the object. Delete selection.
Result included.