Can i change background pictures on forms

Yes. Please check our JotForm tutorial video here 

http://www.jotform.com/form-designer/tuts/episode10/

This similar discussion thread should also help

http://www.jotform.com/answers/168394-Custom-CSS-How-to-setup-a-background-image-around-a-form

Let us know if you need further assistance.

Thanks.