Found another flash. Not sure if its been mentioned or not, but here it is:
On Chapter 2 - The Bridge, a little ways into the level you will come to the bridge,you will then descend stairs then go up another set to get back on top of the bridge.
Moving forward there is a train, hop onto the box on its left side and jump into the train, go all the way to the end of the car and open the red box to your left.
Inside are 3 baby dolls, examine them to get a flash.
*EDIT*- Another on the same level, don't get seen by the military trolly and you get a white flash.
*EDIT*- On a new flash finding frenzy, on Dead City 1, after going upstairs in the first building you arrive in, a Nosalise will run past, proceed forward and look out the last window on the left you will get a white flash for watching it run away.
As a side note I did get this achievement on my first run through, things I didn't do that guide says to do:
-First off I looted all corpses and bodies and got all gold bullets in the cities to get Sherlock.
-Didn't give bullets to beggars besides the one that gives first flash.
-Didn't talk to step dad at Exhibition
-Took Bourbons bullets
-Took all other bullets given to me, except from the Mother in Child.
In the end I think this achievement is determined on how many flashes you get, the golden ones being worth more, while the white ones are worth less, thats my theory anyway.
100% Retail: (x21)
Blue Dragon, Cars, Enchanted Arms, Eragon, Fight Night Round 3, Gun, Jericho, King Kong,
Lost Planet, NBA 2K6, Oblivion, Phantasy Star Universe, Prey, Samurai Warriors 2, Shrek, Superman Returns, The Simpsons, TMNT,
Tomb Raider: Legend
100% Arcade: (x6)
Aegis Wing, Castlevania: SOTN, Contra, Crystal Quest, Golden Axe, Sonic 2