As of build 641 IC2 can dump textures from inside the game into png files.
The command is /ic2 debug dumpTextures <name> <size>.
- name: Game registry name, e.g. IC2:blockMachine.
The name can be optionally followed by @meta-data specification, e.g. IC2:blockMachine@0. If it isn't specified IC2 will try all consecutive meta data values until either the item yields no translated name, one it has already seen or an error occurs.
There's also support for wildcards (*) when specifying the name, e.g. IC2:* will dump (almost) everything from IC2.
- size: Size of the output texture, in pixels. This can be arbitrary as long as it's not exceeding your mc window resolution, but I assume sizes somewhat related to the original texture size look better.
The name format is Sprite_<modid>:<translated name>_size.png. This way you can set your language to en_US and should get well organized names for use with wiki templates.
For the sizes I'd suggest trying something more suited for modern higher resolution displays, instead of keeping to the old ones, e.g.:
- 192-256 px in the block/item page
- 48-64 px in recipes
- 16-24 px in the menu