Exploring the GIA image QA panel
The image QA panel has the following elements:

1 - Project source and target file listing
Shows all files currently selected for processing in the active project as well as matching target files..
2 - Source/target image boxes with zoom control
Displays the selected source and target files. 
3 - Auto-linking control
Provides a convenient and efficient way to associate source files with corresponding target files. For more information about this process, please see Understanding Auto-Linking
4 - QA Status box
Provides information about the mechanical QA status of the selected source/target image pair. 
 
A closer look at the QA Status indicators
The indicator lights provide  information about the mechanical QA status of the selected source/target image pair. 
Source/target size check Indicates, whether or not the pixel dimensions of source and target files match.
Image modified if 'localizable' check Indicates, whether or not only images marked as localizable have been modified. If a non-localizable image has been modified, this indicator will turn red and display a corresponding QA message in the QA comments box (and vice versa).
Source/target frame count check Indicates, whether or not the frame counts of source and target files match.
Source/target file format check Indicates, whether or not the file types of source and target files match.
QA Comments Displays auto-generated comments providing details about error conditions and also allows entering of custom comments by the reviewer.
If any of the indicator lights toggles to red, check the QA comments box for details about the error condition. In the example shown here, the graphic artist saved the target image at a size just one pixel below the source file's dimensions. Normally, such a difference would not be detectable by simply visually comparing the images.

GIA also validates that source and target file formats match (regardless of file extensions), that the frame counts match and that the image has only been modified if it was marked as 'localizable' in the project.