Photography Deadly Item Inventions
One of the first things I wanted to know about to invent in Dark Cloud 2 is more bombs that way I could clear floors that had the kill all enemies with items requirement. This lead me down a similar path of inquiry about all the different items you could invent to help out with this particular medal. There's actually three different sets of bombs you can make ontop of other items you can throw at enemies.
Bomb (Chapter 1)
Candle, Pot and Weapon Shop Sign
The Church in Palm Brinks will have a Candle as well as many other locations throughout the game. Pots can be found in many locations, Parn's Studio in Palm Brinks is one. As for the Weapon Shop Sign you'll need to snap a picture of the sign on Milane's Store.
Improved Bomb (Chapter 2)
Candle, Coal and Egg
Candles are fairly common, one location is inside the Cathedral in Palm Brinks. There's a candle at the end of each pew. Coal can be found inside the Engine room of Blackstone One. This is a missable photo so be warned! And finally an Egg can be found inside Dell Clinic in Palm Brinks. Dell Clinic is located on the lake and as for the Egg it's located on the shelf inside the building.
Final Bomb (Chapter 5)
Candle, Cinders and Oven
The earliest time you can grab a picture of a Candle is in Palm Brinks inside the Cathedral. There are many others though. You can find a photograph of an Oven in Palm Brinks as well - in Polly's Bakery. For the photograph of Cinders check out my Scoop Guide
Lightspeed (Chapter 3)
Candle, Flower and Rock
Candles are fairly common, one location is inside the Cathedral in Palm Brinks. There's a candle at the end of each pew. You can take a picture of a flower inside Polly's Bakery in Palm Brinks (on top of a barrel). As for the Rock photograph - you can find one in Sindain or... well many other locations. It's a rock!
Ultimately, Lightspeeds are total crap if you ask me since they require an item you can't craft to even make them. Making bombs is extremely expensive but the best way to get enough items to always accomplish your goal. For a majority of the game Improved Bombs will cut it and you won't have to spend the extra on Final Bombs. I only used some Final Bombs in the last dungeon and generally I just used what I found since the improved ones were so expensive to make.
I highly recommend you clear out the Item Medals periodically throughout the game - usually I swung through one or two floors of them after finishing each dungeon that way I wasn't overflowing and unable to pick up the weaponized items I found while exploring.