Help with adding a custom plugin

[eluser]DumpProgrammer[/eluser]
I have an image resizer plugin that is usually loaded by using an include file on every page that its required. Here is the code you would use on your images

Code:

<IMG alt="" src="/scripts/timthumb.php?src=/images/whatever.jpg&h=150&w=150&zc=1">

Here is a link to to the script page. I need help with where I should put the custom php script whether it should be helper, library etc.