When it comes to names, "Theresia's Vow" by itself is not sufficient. Ideally, the image name would include the manga episode it comes from, then a name related to the image's contents, then the medium. In this case, it would be "E0H-Theresia's Vow-Manga". This way, the image is easy to source. All updated articles on the wikia have images named in this style, although many images on the wikia that were uploaded before these guidelines were introduced just have descriptive titles, or are jpgs with no descriptive names at all (only a series of numbers or something like that), which we try to avoid. PNGs are preferred over JPGs, as Besty said.