I had an interesting bug to fix this week, discovered in the context of a SharePoint application, but that equally affects anyone producing content for display on the web. The client I've been working with recently has been having trouble displaying marketing images from a SharePoint picture library. Given that the picture library in question was customised quite heavily (to include custom columns) as part of the solution I've been working on, my first assumption was that there was an error in the provisioning code. The library in question was working perfectly with many of their images - photos of members of staff had been uploaded without trouble, and the two standard size thumbnails had been generated automatically as normal. Clicking the images from thumbnail view (where small thumbnails are displayed) of a picture library takes you to the detail view for the item (where the larger auto-generated thumbnail is displayed). At that point, clicking on the image once more should take you to the full-size image file itself. Photos of staff were displaying correctly, but marketing shots of swirly things and pretty patterns weren't displaying correctly.
After a fair bit of investigation, I discovered that those images that refused to work with SharePoint couldn't be opened in IE at all, though Windows would happily preview the image for me. When I attempted to view the image in Paint Shop Pro I had a strange error message about the colour profile information, and that's when things started to become clear. After some chatting with James, we discovered that the .jpg file had CMYK metadata, instead of RGB. So, this was a CMYK JPG, not an RGB JPG, and that's the problem. If you want to view a CMYK JPEG file in a browser, you need Safari or Opera (at time of writing), or possibly some kind of plugin, if one exists, that could fix this issue on IE or Firefox.