There are operations for accessing an external web page internally. You could do this with raw sockets even if you have to (
Connect to the server,
Request the image,
Receive the image,
Cast some black magic).
Make sure to use the correct header information to request the image (
GET /myimage.jpg HTTP/1.1\r\nHost: mywebsite.com\r\nContent-type: image/jpeg\r\n\r\n), and then use your file IO functions (
Open File,
Write to File,
What the hell does this do?) with a binary write stream to save the image locally.
Then, of course, automate this with an hourly
crontab.