Does not nature itself teach you that if a man wears long hair it is a disgrace for him, (1 Corinthians 11:14)
Why is Jesus often depicted in paintings with long hair, if it's disgraceful for men?
Even if the premise that Christ had longer hair is true, it would not matter as that is not the point of this passage. If it is read in context i.e. read the chapter before and after, it is clear that Paul is talking about how Jewish customs and how even though they are no longer necessary due to Christ's sacrifice, they should still be observed if you are causing your brother to stumble:
Then he goes on in the start of Chapter 11 to talk about the custom of women covering their head to worship and men uncovering their head to worship and why that custom was in place: because angels needed to cover their head out of reverence to God. I'm not a Jewish custom expert but I do know that the point of this passage was not to show that it is disgraceful for men to have long hair but to show that you must respect the customs of the people you are around in church. This is shown by the ending phrase of that section:
It is important to always read God's word in context as it was meant or else you run the danger of missing the point.
Hope this helps :)
Being as there is no image of Jesus that has any historical credibility, the question is based on a faulty premise. We simply do not know what Jesus' hair looked like.
The paintings to which you allude tend to be those painted by the European masters in the 16th & 17th Centuries. At the time, it was fashionable for men to have longer hair, and thus it was not "a disgrace".