Extract files from game.

[Bit Strange]

You should be able to get the game's textures by opening the PPSSPP program and going to:
Game Settings > More Settings > Tools > Developer Tools
and then turning on 'Save new textures'.

After that, start playing through the game.
As you play through the game, textures will be put into a folder.
This folder is located somewhere in the same folder as your PPSSPP:
ppsspp > memstick > PSP > TEXTURES > (The ID of your game) > new

Hope this helped.