It is a sad but true fact that once you've started cosplaying in public one thing is inevitable: your photo will end up in a public forum, and soon after all sorts of bullies will come out of the woodwork to rip you apart. No matter your skill level, weight, or attractiveness you will be criticized for poor craftsmanship, being fat, and being ugly. If heaven forbid you are too tall, too short, a different ethnicity, or a different body type than character you are trying to portray, this will be pointed out as a negative factor. It's almost bad enough I might suggest to never read the comments on a public photo of yourself, especially if you did not post it, however at some point we all get curious. It is my hope, though, that before that happens you can have a little perspective and a think skin toward such stupidity, because it honestly means NOTHING.
One of the very worst things to come out of the internet is the false bravado it gives people. Things they would never dream of saying to someone's face suddenly roll off the tongue (or fingers, as it were) with ease because they don't have to directly confront the reality that those photos are of real people with real feelings. It disconnects them from the situation so that they can build themselves up without consequences.
I've always been told that bullies are insecure or jealous of their targets. They feel threatened some how, so they put others down so they can delude themselves into thinking they're better. I don't have any sort of degree in psychology so I can't say for sure, but it sure makes sense. Chances are, that girl calling you fat is actually paranoid about HER weight even more than you, and that boy who called you ugly is jealous he can't pull off an awesome costume like yours. For every negative comment you might see, remember all the positive ones you've gotten, and remember all the friends you have who love and admire you. What should you care about what some stupid anonymous person on the internet thinks? They don't have the guts to talk to you in person, so they don't matter.
Bullies only have as much power over you as you let them. Outside of your emotional reaction, anonymous cyber bullies don't have any real way to affect your life: they don't interact with you in person, they can't influence your friends, they don't talk to your boss/teachers/etc. If you don't see what they write it's as if it was never written. That doesn't mean it never hurts, but keep things in perspective.
Bullying is a horrible aspect of our society. On some level I think it is a symptom of how desensitized we've become by all this technology. A picture is not a person, it is a picture. Pictures don't have feelings. We forget that picture represents a person, and that person does have feelings, feelings which can be hurt. I truly hope none of my readers have ever stooped so low as to put down another cosplayer in a public forum on the internet. If you have posted, or ever consider posting rude insults of another cosplayer (or heck, any person) in a public forum on the internet please think for a second. Remember this is a real person. Remember they can see what you're writing. Think about how your words will make them feel. Think about how YOU would feel if someone wrote those words about you. If you see a friend posting bullying comments remind them to think about what they're doing. As much as we can grow a thick skin and shake these things off, they DO hurt. As silly as it can sound, there really is something to be said about that old cliche: If you can't say something nice, don't say anything at all.
I hope if you ever come across someone else ignorantly insulting your image on the internet you won't take it to heart. It's not worth it.