Can I transfer photos from iPhone 4 to a MacBook via Bluetooth?
I know you asked if it was possible over Bluetooth and although my research didn't turn up anything for non-jailbroken phones, here is a WiFi solution which you could use on an Ad-hoc network that would work effectively the same way.

Non Jailbroken


WiFi: WiFi Photo Transfer (App Store)
iPhone to iPhone: Bluetooth Photo Share (App Store)


Jailbroken


iBlueNova (Cydia)