For one it's a bit of a cultural standard - like appearing in a suit for the interview; it doesn't show your qualification, but it shows basic etiquette (it's no longer as usual as it used to be and not the best example, but I think it gets the point across). Also, an image helps you form a more personal connection to a person.
But I'm not a recruiter myself, so take that with a grain of salt.
But I'm not a recruiter myself, so take that with a grain of salt.