It is not logical to think that while Jesus was advising the disciples about the using of long clothing by the scribes, he himself was wearing one of them. At the time, robes and long clothing for men was a sign of useless luxury. It didn't become to Jesus to be clothed like that. Especially when he was saying what we read in the former two verses.
If we read John 19: 23 we will see that Jesus' tunic was made of only one piece, something like a tube. Therefore it couldn't be that long because it would hinder walking freely.
"Then the soldiers, when they had crucified Jesus, took His garments and made four parts, to each soldier a part, and also the tunic. Now the tunic was without seam, woven from the top in one piece." ( John 19:23 )
In short, pictures depicting Jesus in long clothing and robes are out reality. The misrepresentation of Jesus had been so general, that this concept of a Jesus dressed in short clothing, like a Hebrew labor, or like a Roman soldier, would not be easily accepted by the vast majority of Christians.