1. Click the photo you want to share
2. Scroll down and on the right where it says "addition information"
and click "different sizes".
3. Choose the size you want
4. Scroll down and choose option 2 - grab the photos url.
You can now take this URL and put into the appropriate box.
On KH -
If you want to add an avatar to your user options from the link on the bar right above the yarn ads. Click "edit avatar" and use option 1 to add the URL from Flikr.
Is this what you wanted to do? Once you can do this you follow this same basic pattern. Hope it works for you.
When asking questions ALWAYS post the name and a link for the pattern if you have it.