Missing images

[Perfidus]

I would like to know if there's a way to substitute missing images with an alternative graphic.
My web has lots of images but the source is given by php, sometimes PHP thinks an image is there and it calls the image but what it gets is the famous red cross of missing picture.
How can avoid that?

[pyro]

Check if the image exists: http://us3.php.net/function.file-exists