Python Reference Implementation

# import code for encoding urls and generating md5 hashes
import urllib, hashlib

# Set your variables here
email = "someone@somewhere.com"
default = "http://www.somewhere.com/homsar.jpg"
size = 40

# construct the url
gravatar_url = "http://www.gravatar.com/avatar.php?"
gravatar_url += urllib.urlencode({'gravatar_id':hashlib.md5(email).hexdigest(), 
	'default':default, 'size':str(size)})