If you guys are close, just saying "hey, I saw your pics the other day by accident, and I gotta say you're really hot!" is totally fine! Just because one is good friends, doesn't mean we can't find each other hot. That doesn't automatically ruin a friendship, and it could add another dimension to the friendship.
Try not to overthink this. If you guys really are as close as you describe, then you guys will get through whatever it is that you decide to express/show. So try to stay honest to how you feel and acknowledge the complex feelings you have. Don't try to shove things in your unconscious because you think you need to be a certain way towards this friend, because that would most likely be harmful towards both you and others in the long run.