The program will build a session based on the number of trial types and starting with the first image ("1.bmp").  For successive discrimination, it will increment by 1 so that every odd image is an S+ and even images are S-.  For simultaneous discrimination, images will be grabbed in pairs (1 and 2, 3 and 4, etc.) and the first image in each pair will be the S+.
Put only the images you want to use into the "In Use" folder.
The last three images in the "In Use" file are priviledged (ready signal) and (response markers) and must always be present. If you have 68 images, then they should be 68, 69 and 70.  
The first image in your set (of n images) must be 1.format and continue successively (e.g., 1-7).