There are 176 CGs. Most of them are unlocked through the good, bad, and happy ending routes of each of the five characters. Some sequences have multiple images associated with them and have to be replayed to get the variations.
Below is a video that shows the 176 images. It focuses on the frames that have more than one entry. If you are missing one or more of the images, you can use the list below to go to the appropriate part of the game and replay a sequence. Note that, as stated above, you might have to replay the same sequence more than once to get all the variations of a CG.