If you want to optimeze your website for mobile devices, you should use these css codes for all your major images like logos or banners.
1 2 | width: 100%; max-width: 100px; |
For an image, you should have:
1 2 | <img src="files/img.jpg" style="width: 100%; max-width: 100px;"> |
100px is the maximum size of your image, you should measure it and put its default size.
Then go to http://quirktools.com/screenfly/ for example and test your website.