The mint mini length comparison shows a short relatively straight edge, making the difference from a lower hem below the knee easy to identify.
Clearly visible round reflective elements dominate the surface while the lower edge stays relatively simple. For the length comparison, first consider the gap between this short edge and the footwear area, which is not fully pictured. Do not invent a missing matching shoe combination as fact. Use your own pair when trying a similar shape instead, so the decision remains connected to a complete outfit.
More leg remains visible below this skirt than beneath a midi. Whether you want that for your evening is personal rather than a rule about height or leg shape. The image helps describe the difference between a clearly short outline and a longer one. It does not automatically expand the meaning of midi.
The diagonal shoulder line and dense round decoration are other visible details. They may influence your choice without obscuring the length question here. Compare short and longer shapes with the same intended shoes and a similar camera perspective wherever practical.