Can not make this image downloader work

[snippsat]

There are several problems here,so not even close to work
Before writing more code most test that what you get back is acutely usable.
print() always work as fast test,or here i use pprint() then is easier to look at content.

import requests
import bs4 as bs
import urllib.request
from pprint import pprint

url = 'http://legacy.lib.utexas.edu/maps/topo/indiana/'
opener = urllib.request.build_opener()
opener.add_headers = [{'User-Agent' : 'Mozilla'}]
urllib.request.install_opener(opener)
raw = requests.get(url).text
soup = bs.BeautifulSoup(raw, 'html.parser')
imgs = soup.find_all ('img')
pprint(imgs)

Output:
[<img alt="The University of Texas" src="/images/globalHeaderFooter/university_seal_informal.png"/>,
 <img alt="The University of Texas" src="/images/globalHeaderFooter/UT_Libraries_RGB_inf_brand_b2-ac.svg"/>,
 <img alt="" height="3" src="http://legacy.lib.utexas.edu/graphics/orange.gif" width="5"/>,
 <img alt="" height="3" src="http://legacy.lib.utexas.edu/graphics/orange.gif" width="5"/>,
 <img alt="" height="3" src="http://legacy.lib.utexas.edu/graphics/orange.gif" width="5"/>,
 <img alt="" height="3" src="http://legacy.lib.utexas.edu/graphics/orange.gif" width="5"/>,
 <img alt="" height="3" src="http://legacy.lib.utexas.edu/graphics/orange.gif" width="5"/>,
..... ect

As see this is not images links of maps that you want.

So can help write the start as this is not usable.
I gone trow awyay urllib as that should not be used anyway.

import requests
from bs4 import BeautifulSoup

url = 'http://legacy.lib.utexas.edu/maps/topo/indiana/'
response = requests.get(url)
soup = BeautifulSoup(response.content, 'html.parser')
maps = soup.select_one('#actualcontent > ul')
map_link = maps.find_all('a')
for link in map_link:
    print(link.get('href'))

Output:
http://legacy.lib.utexas.edu/maps/topo/indexes/txu-pclmaps-topo-in-index-1925.jpg
http://legacy.lib.utexas.edu/maps/topo/indiana/txu-pclmaps-topo-in-bedford-1934.jpg
http://legacy.lib.utexas.edu/maps/topo/illinois/txu-pclmaps-topo-il-birds-1914.jpg
http://legacy.lib.utexas.edu/maps/topo/indiana/txu-pclmaps-topo-in-bloomington-1908.jpg
..... ect

So now can try to figure out how to download these image links,and you do not need to import urllib for this.