I don't mind when people do it except for creepers of course.
If we're cosplaying from the same series, it is even better. If I see someone that's cosplaying from the same series as me, I will go up and get a picture with me in it because it makes sense. The random, characters from different series,shots can be really funny too.
Of course, it's good to set boundaries for yourself of what you are willing and not willing to do with others in a picture.