..................In other words, it seems to be very easy to pirate images on any website..................
Basically , if someone can see it they can copy it. Even watermarks aren't impossible to remove in Photoshop.

In the meantime should I delete, & re-upload downsized jpgs what will happen to my 3 original competition entries ?
Seriously... you can always do a print screen and copy/paste it into a new file. It is impossible to protect your files completly. So many worldwide media companies tried it, but the copying still continues...