Here you go -
- Click the photo you want to share
- Scroll down and on the right where it says "addition information"
and click "different sizes".
- Choose the size you want
- 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.