The file size of your pictures is most likely too large. You can use a program to reduce the file size, or, when taking photos for posting on this website, set your camera for "basic / small". You are probably now using the " large / fine" setting, which provides a large file size for printing and making enlargements, but is over kill for Internet use. File size could best be described as the amount of digital information in the picture. Too much makes for slow uploads, and often exceeds the file size limit for websites such as this one.
Larry