Epson CX6500 Reference Manual page 339

Select a desired button from the Select an event list. Select Start this program and select the
desired application from the list.
Note:
If Prompt for which program to run is selected, when the button is pressed, a
dialog box appears to prompt you to select an application from the list.
Some applications do not support linkage to scanners and digital cameras. Linkage
is available only for applications which appear on the list.
To save your settings, click Apply and
OK.