Hi Norlisa, Your photographs are automatically covered by copyright laws at the point of creation. This applies to all creative works. As for protecting it, that's a different matter.

In order to upload to most stock photography sites, someone needs a high resolution copy of the image. Medium reduces the size of images when you put it on your blog, so they are low resolution copies.

This should stop anyone from taking your image from medium and putting it on a stock photography site. But it doesn't stop other bloggers from using it illegally.

A lot of people steal people's photos off the internet and think if they have a right to use them, especially if they credit the source. That's not true. But trying to stop them is virtually impossible. Some end up in court.