If you haven't heard anything lately about this issue, then I suggest you read this and take heed.
Recently, a certain photographer has been taking photos at conventions, having clients sign an agreement and then taking those photos and using them on fetish pillows without the permission of the clients...I am sure you can find all sorts of articles about it right now if you google it, but I think the major thing to take away from this is to be careful not to sign anything that may permit people to do this kind of thing to your image without your approval.
In reality, you really should not have to sign anything to let people take your photo. If they are using it because they want to use it simply to promote their photography skills, then you paying and volunteering to let them take your photo is enough to show off their skills. Basically, if someone makes you sign something to take your photo, it's sketchy and you're probably giving them rights to do things that you really don't want to be done to your image.
As a cosplayer, I am absolutely appalled that someone thought it would be okay to deface people's integrity like this. There are both male and female shots, so there is not any kind of gender issue here, but I think it is key to note that if someone is wearing a costume that shows skin, that does not give any person the right to degrade their costume that way. It's within the nature of comics and anime, that costumes/clothing often are somewhat risque, but at any point and time, is it really any different than wearing a bathing suit?
"Sexy cosplays" don't deserve to be sexualized like this and I think the main fall back from things that happen like this is the feeling of not being safe. Cosplayers often get their photos taken, but what kind of world will cosplayers have if we have to worry about every Tom, Dick and Harry taking our photo or looking at our photos online.
Cosplay does not mean consent.
We need to make sure we're helping each other and making sure we promote a safe environment for future cosplayers, or else the entire community could fall to eroticism and an overall uncomfortable environment.
No matter why someone is cosplaying or what their cosplay costume looks like, please have enough respect for the person in the costume.
Thank you; god speed. *Ends Rant*