import requests
from bs4 import BeautifulSoup

r = requests.get('http://dota.reactor.cc/tag/Dota%2BArt/new/649')
content = r.content
soup = BeautifulSoup(content, 'html.parser')
response = soup.find_all("a", attrs={"class": "prettyPhotoLink"})

for item in response:
    print item.select('img')[0].get('src')