To access image-specific settings, hover on a thumbnail in the main jAlbum editing window, and click More.
Then choose Edit.
Then choose the Atom panel on the right side of the editing window.
Note that the dimensions of the video window will accept these width and height entries unless they are larger than the selected jAlbum image bounds, in which case they will be automatically adjusted downwards to remain within those bounds. The adjustment occurs at album creation time - the adjusted values are never displayed in this window.