[Plugin: WordPress Form Manager] Changing the Submit Button to different images

I use this plugin for different clients. I’ve tried customizing the css a little.

I’ve found that the label { & the input { can control the text, the field, and the button.

Is there a name I’m missing to just control the submit button. I would like to use an image for the submit button.

Would you tell me how to do this or direct me on where I go to do this.

http://wordpress.org/extend/plugins/wordpress-form-manager/