What the quality checker does
A QCer is the final defense against mistakes in any group's releases. Choosing to skip this step of scanlation often results in a higher number of mistakes in your releases compared to groups that go to the trouble of having some quality assurance.
What you will need
An image viewer such as Mangameeya, ACDsee, XNView, Comicrack, etc.
Notepad 2 or other document creation software.
A copy of Photoshop (depends on the QC style)
The two types of QCers
There are two types of QCers. The first type checks the releases for mistakes and creates a text file noting the necessary changes the typesetter/cleaner should make. The more common type of QCer, however, looks over the manga and makes the changes to the .psds themself.
Steps to follow when Qcing
Check for editing mistakes such as specks, unclean bubbles, uncleaned text, bad brushing, overlevelling etc. (QCers are usually retired editors who know what they are doing)
Check for grammatical, spelling, punctuation and typesetting errors.
Check filenaming and take care of the final preparation of the images. (save as png, etc.)
QC Tutorial (by ruinevil)
Notepad 2 (Great improvement to notepad)