Jstorck,
The Item ID (which appears on the PayPal receipt) needs to be unique to identify the actual image it is associated with. Since Shozam does not allow two images with the same file name to be added in an album, the program uses the file name as the unique ID for the image. This has the advantage of not burdening the user with assigning a unique ID for each image.
If you would like the program to behave differently, such as stripping out the file extension, please post your request in the Wish List forum and provide more details as to why you would want the program to behave that way. Then we can use the information when we review the various feature requests.