I just received an email from a nice guy on flickr, warning me about the fact that I had saved my images in large file size online, it made it easy for them to be downloaded and basically used without my knowledge or consent. Now for you guys who don't know me, I do not have a clue when it comes to anything technical and computers and me are an incredibly scary combination!!

So what I basically need to know is ...

1. should I save in two different sizes, 1 for online and 1 for printing??
2. how & what size do I save in, that will also work for uploading to AP.
3. should I start to add a watermark to my images to help protect them??

Sorry for sounding really stupid, there are some things I'm good at but its not computers