Some links to free stock images:
http://www.stockvault.net
http://www.sxc.hu
Not free but very reasonably priced
http://www.dreamstime.com
Some tips:
The size you need is: 700 by 300 pixels exactly. If you ignore this your image will be distorted and will not look good.
1. Always choose image that is larger than 700 by 300 and be aware that some cropping will occur.
2. Never take a smaller image (let's say 300 by 150 pixels) and enlarge it.
3. when resizing an image leave the "keep the proportion" box checked.
How to do it
You don't have to have Photoshop to resize and edit images. These are quite a few great (and free) online applications.
1. go to http://www.picnik.com
2. upload your image, hit edit button, then "resize" and that's it.
There are also other easy to use options – just play around!
Design:
The label is fairly small so something that has a distinct shape and good contrast will look better.
I hope this helps
Inguna