We sometimes have clients uploading JPG images in CMYK rather than RGB. Some browers don't like the CMYK images and displays the color all wrong. Is there an easy way to convert and image to RGB using the GDI?

The CMYK Color Gamut is within the boundaries of RGB's Color Gamut.

You might encounter issues with metals.  For instance a silver CMYK print-out will never really look right on RGB.

My recommendation: increase the brightness and contrast on CMYK images.  There is no way to tell if an image is CMYK unless it is specified in a filename.   

No you don't understand. IE will not display CMYK JPG images AT ALL. Changing the brightness will not do anything. These images are not going to print, they are just for display on the website. Here's an example for you: It's the same image, in CMYK and then after conversion to RGB (I used Photoshop to convert it to RGB)

http://www.6nf.com/cmyk.jpg
http://www.6nf.com/rgb.jpg

In my IE and FireFox the CMYK image comes up as just a broken image. If you download it to your desktop and open it with anything else you'll see it's actually fine.

So my question again:

Is there a way in GDI+ to convert CMYK JPG images to RGB JPGs?

Yes there is. I had the same problem and I had a VERY frustrating time finding a solution. Finally after 2 days and over 16 hours of research I was able to put together the solution documented below. I hope it helps. Let me know if have an answer to the "Detection" problem at the bottom of the tutorial. http://www.maxostudio.com/Tut_CS_CMYK.cfm