Ha, yes, I see. I see . There is a difference in meaning when you consider the picture sentence. But what is odd is the 's'.

A picture of my sister's. The s looks like a leftover from his.
"My sister his picture". But then my sister is a her. Then I do understand you can't write or say " my sister'r picture".
You could say though: "my brother's picture = " my brother his picture", hey ho ! Sinking deeper and deeper in the mud. eek