Possible "reaching for it" explanation?
As I recall, it was established in The Time of Angels that the ones from Blink were weaker scavengers, needing to feed off people's temporal energy to sustain themselves - which is why they threw people back in time instead of outright killing them like the one in The Time of Angels.
Which of course makes some of Ten's lines in Blink no longer make sense (he implies that they always "kill" by temporal displacement, the nicest psychopaths in the universe), but we'll go with it.
Maybe because the Angels in Blink were weaker, they weren't able to "transfer" onto the pictures Sally Sparrow took?
That's assuming you have to make it work out perfectly. I think "that which holds the image of an Angel becomes itself an Angel" is better left not too closely examined, just use it where it's effective.
Or, for a totally other possibility - and I have to thank TVTropes for this one - what if the images DID become Angels? Specifically, the very Angels that ambushed the Doctor and Martha, sending them back in time but stranding the TARDIS. Thus creating a stable time loop.