Possible to run a shell script via the context menu of a file?

Hello,

I wrote a nice little shell script to resize and watermark images. It has an integrated file selector, but I thought of an idea to save the file select part:
I would like to select the image in the finder, right click on it and run the shell script from right there, passing the selected image as parameter.

I already tried to create this using the "open with" dialog, but it won't let me select ".command" files.

Thanks alot for your help!
Philipp

Create a Service. This will get you started: http://www.makeuseof.com/tag/how-to-create-your-own-services-menus-mac/
Not a right-click but just Finder menu-Services. Don't know if Applescript will select .command files but should have a Run Shell Script command.