Go to your 'my profile' page.
Click on "General info about myself"
On that page, there will be a line for picture.
Enter the source of the picture into the blank space.
Hit the "Submit" button at the bottom of that section.
That should do the job.
Seriously? That's what you're going with? I prefer this tiny ad:
Edible Landscaping With A Permaculture Twist/ Second Edition - Kickstarter