The long green dress comparison shows ruffles along the open front and a rear length resting on the floor instead of a free midi edge.
Ruffles frame the neckline and continue down the front opening. Beside the visible shoe, considerable length reaches the floor and continues behind it. A picture with an uncovered front leg therefore need not show a short or medium-length overall dress. That distinction is precisely what makes this reference useful within the comparison rather than another interchangeable midi example.
When looking for a midi, it helps specify what lower outline you do not plan: a rear area on the ground and a line continuing to the floor. That describes your intended use without judging the long dress. You may still enjoy its upper ruffle shape independently of the length.
A real long model would require checking the front opening and rear area separately. Here, the visible difference from the black midis’ free lower edges is sufficient. Make your final comparison on the actual outfit in your own shoes; the background and photographed pose cannot replace that decision.