If it's the same ad as the one where people hold photos in front of their faces and the the photo becomes "real" - it's "Picture Book" by The Kinks... from their"Village Green Preservation Society" LP, 1968. Just been reissued on CD too.
Nice one... I THOUGHT it sounded like the Kinks... Haven't got that LP, I'll have to check it out. Sounds remarkably modern for a 68 tune... the intro is very like that of the Apple iTunes ad
Cracking album - sank like a stone when it first came out, but has since been correctly re-evaluated as a lost classic. Ray Davies is my all-time songwriting hero - you can keep yer Lemon and McCarthy or whatever they're called :O)