You said you have a reference to it so this is probably the issue:
You are referencing the JQuery scripts again in the page, thus overriding the Shining Image plugin which declared before the second reference.
JQuery plugins extends the JQuery object, So if you reference JQuery again it overrides the “extended” JQuery object.
Check the rendered HTML, you probably have two references to JQuery library
Check this question, I adjust my answer a bit, it looks like the same problem
Or you just added the reference to the plugin before add the reference to the JQuery it self, which explains why you’re having problems…
solved Shining Image jquery plugin not work