I really don't know where you got the idea that he was saying that one can divine some knowledge from a painting or that paintings and culture influence our sexuality.
Edit: Spelling and punctuation. God, I really should enable a spellchecker. I'm a terrible speller, I apologize.
Berger discussed the nude as a convention that tells you about ownership, power, and who the picture was made for.
Claude says that's chapters 3 and 5, so I'm fairly sure my memory serves.
That said, your summary is accurate. These claims aren't the primary topic of his work, so maybe I am being overly harsh on Berger.
Still, the claims have been influential. They do belong to him. And they've led to all manner of supposition about art, history, feminism, and human behavior.