I found some sites with 30+ examples of headers and got a few ideas flowing. I didn't have any specific idea/style in mind, that was the problem.
The overlap effect I'm talking about is in so many different headers, I decided to go with a stock photo of a dog which I've made appear to be leaning over the bottom 'border' of the header, so I'm good for now.
Some sites that helped me get ideas flowing, for others who find this thread:
http://sixrevisions.com/web_design/five-types-of-effective-headers-in-web-design/ ('overlap' example on the top one)
http://www.1stwebdesigner.com/inspiration/trendy-unique-website-header-designs/ (these are a bit over-the-top but opened up the possibilities for me)
I've had to get much more familiar with image editing software than I planned to, never liked graphic design much.