Razz, double check your image's resolution. Resolution doesn't mean squat on a computer screen. A 300 dpi/ppi image that's 200px by 200px will display the very same image at the same size on your screen as a 10 dpi/ppi one will. The larger the resolution of your image, the bigger the file size will bloat up. Drop the resolution in an image editing program to make the file size much more manageable.*
*Photoshop's default Scale tool will change the image's dimensions along with the resolution. Toggle off "Resample Image" to prevent this from happening.