What black cartridge does the Canon MP830 use for photos? -

There are two cartridges. The PGI-5bk and the CLI-8 black. They are both black cartridges and I know one is for photos and the other is for text. The PGI-5bk is bigger so I would assume it s the one used for text, and the CLI-8 one for photos, am I correct?

Yes.