what happens to a photo when I post it here

I've been experimenting with what happens to a photo when i post it here. I had made a large file for my daughter to print at school. it was a jpeg but i'd saved it with a resolution of 300 and kept the size at about 5 by 5. When i uploaded it here and then right click to save back on my hard drive, the fine folks here at blogspot had kept the dimensions but dripped the resolution to 72. So this is definitely not the way to share a file that you want your grandma to download and print. This is very interesting!