iPhoto only supports RGB images (remember it is designed to work with point and shoot digital cameras and that is what they create) - sRGB is the best for iPhoto and iPhoto print products
It does not work with CYMK or gray scale images
see
http://www.apple.com/support/photoservices/preparation_tips/
Specifically:
What image settings should I use when preparing my images for printing?
Although iPhoto and Aperture accept other file formats, your images should be in JPEG/JPG file format for the best results when ordering photo products using iPhoto or Aperture. You can use an image editor to convert your image file into this common file format. _*Also, the image should be in RGB mode, not CMYK.*_ There is no maximum size limit for image files, however larger files can take longer to transfer, and there is a greater chance the image might be corrupted during the transfer process. There is no benefit to submitting larger file sizes.
Is that "without a doubt" enough?
LN
