How to avoid serving CMYK to Internet Explorer?

[smantscheff]

I'm using Coppermine for a database of pictures for publication, for the web as well as for print. Therefore users do not only upload RGB pictures but also CMYK. This works fine except for IE 7 (and below) because this [censored] piece of software cannot handle CMYK.
I added the option -colorspace rgb to the arguments of /usr/bin/convert and this works fine for preview images. The full size image remains in CMYK, though, and cannot be displayed in IE.
My question is: Where do I find the code for displaying the full size image? I'd like to add a browser and picture format test to it so that in the pathological case of IE/CMYK a download link to the CMYK image can be displayed instead of the image itself.