From here you may upload a single JPEG image, or a ZIP archive containing many JPG images.
How to create a zip file of multiple images
On Windows XP, Windows Vista, and newer...
Add your jpg images to a folder, then right click on the folder and select "Send to > Compressed (zipped) folder". You will end up with both the original and a zipped copy.
On a Mac...
Add your jpg images to a file, then just CTRL-click on the file and select "Create Archive". You will also find the option in the File menu. Either way, you will end up with both the original and a zipped archive copy.