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If else condition image field for other css class

Sometimes i use for pages a header image with the simple Drupal 7 core image field. I put the node title with CSS position: absolute; over the header image. But i have a style issue if no image is uploaded. I need a css class which say "no-headerimage" for example in the title. Then i can give for this condition a CSS position: relative;

See here:
http://www.neofelis.de/drupal-commerce (without header image)
http://www.neofelis.de/e-commerce (with header image)

Do anyone know a solution?