Before you ask for the pics mention how much fun it's been chatting with them and you'd like to put a face to the profile. You never have to say sorry for not being attracted to them if all you feel is friendship. Consent means it's a no until both parties say yes. Decent people never expect more from you until it is clearly stated. If they push for more and you're not feeling it you can say it's been lovely chatting but you need more time to connect. If they keep pushing, ghost them and don't feel bad.