Doki Doki Literature Club! contains several files and sections of code that are not used in-game.
house.jpg, located in
images.rpa/images/bg, is a background that goes unused in-game. It was presumably used as a placeholder before the game's final background art was made. The image itself was made by artist Fatelogic, uploaded on 12 April 2012.
In his DeviantArt post, Fatelogic noted that he used Google SketchUp, Photoshop, and "some rendering programs" to create the image. The same house model and angle are used as in this 2011 tutorial by YouTube user Uncle Mugen. This technique is similar to the one used by DDLC background artist Velinquent to make the final background images.
credits_temp.png, located in
images.rpa/images/menu, is an image unused in the game which appears identical to Yuri's third CG, but is slightly lower quality.
credits_temp1.png, located in
images.rpa/images/menu, is an image unused in the game which appears to be a low-resolution prototype version of Yuri's first CG. The background is only sketched, and Yuri's shading differs from the final image.
old is the name of a folder present in each of the four characters' sprite folders (
images.rpa/images/[character]). It contains sketched versions of each of the characters, presumably used for testing before the final assets were drawn.
old2 is the name of a folder present in each of the four characters' sprite folders (
images.rpa/images/[character]). It contains the final character sprites split in half as well as the characters' action poses. The files in these folders likely went unused as the method of drawing the characters increased in complexity from two images to three during some point in development.
In the final game, non-action poses are usually drawn by stitching three files together: the left, the right, and the head. This is so that dynamic poses can be matched with facial features without having to create full image files for every possible combination. For example, Dan Salvato notes in the DDLC Fanpack that Sayori, with 25 faces, 2 left sides, and 2 right sides, has 100 possible combinations for poses. He continues to explain that Natsuki has 155 combinations as a result of having two different heads (front-facing and turned) as well as an action pose.