First, you will be asked about the characteristics of the jpeg file you want to create. Then, the software will ask you for a file name. The names of the actual files that will be created will be the name you indicate, but with a number added at its end. For instance, if you ask for the file to be called "westcar.jpg", the actual names will be "westcar1.jpg", "westcar2.jpg", etc...
Note that I've experienced memory problems with jpeg file creation. The memory demands of java for images is huge, and the default virtual machine "only" use 64m of memory. You might want to start java with the option -Xmx :
java -Xmx128m jsesh.jar