iOS app to transfer images, photos to another phone via Bluetooth
The iPhone 4 does not support the Bluetooth OPP profiles which you need for standard device to device transfers. All you have available are 


HFP (handsfree)
PBAP (Phonebook access)
A2DP (advanced audio distribution)
AVRCP (av remote)
PAN (Personal Area Network)
HID (Human Interface)


Peer to peer comms are possible over BT but the app has to implement the protocol stack itself