What happens when I save an image on my iPhone with no space available?

So I was going around and saving images on my iPhone, looking for a cool wallpaper, and realized after, that I had 0 bytes available before saving the images. I'm kind of worried as of how my iPhone found more space to save these images because when I deleted all of the pictures I had just saved, I had more space than I had started with. Does anyone know what my iPhone may have deleted or how it found more space than it even had.

Root your iphone… Look for google. You will save million of million bytes my rooting.