If you assign a "name" and "value" attribute to a standard button, the request parameters will include a name/value pair containing that name and value. My preference, since the "value" attribute is also used by the user agent to render the screen, is to ignore it and give buttons unique names; then, check which one is present.
For image buttons, the name will be used, but ".x" and ".y" appended, along with the coordinates of the mouse click. Most of the time, you don't care about those, so just ignore them... but again, use the button's name attribute to identify it. That is, if your HTML says "<input name='
test'>", just check the request parameters for a parameter with the name "test.x".
HTH