Simple scrollbar functionality

hi, i created a horizontal scrollbar using the simple custom scrollbar tutorial. it contains several different thumbnail images that move left to right with arrows. so basically it is the same as the tutorial, except it is horizontal and contains images with rollover functionality instead of text. i am wondering if there is a way to remove the rollover functionality when part of the thumbnail image is hidden by the mask? right now, when you scroll you can have maybe an edge of a thumbnail visible and the rest hidden by the mask, yet still click on it. i want to stop that from happening…can anyone help? thank you!