Hot linking.
What is it?
Linking graphic images from a host website to another.
Why is it bad?
Each time the image is viewed at all the various locations it has been linked to, it causes a request for bandwidth usage at the original site. The owners of that site are billed for bandwidth used by their site. When their monthly bandwidth limits are reached, their site gets shut down by their service providers until additional bandwidth is paid for.
How do sites prevent it?
When too many people have hotlinked to an image causing a spike in bandwidth usage, website administrators of that site often remove or move the image to break the hot links and end the theft of their bandwidth and prevent shutdown of their website. This results in the broken image displayed in the post here on A2K.
Why does it not happen to all images from a particular site?
The popularity of the image with hotlinkers is not enough to cause a spike in bandwidth usage so the URL isn't changed to cause a broken image.
How to get around this to post images on A2K:
Create an account at any one of the numerous free image hosting sites and upload a copy of the image there after downloading it to your device. Obtain the URL for the image at your account and use that for posting images at A2K.
By doing this you'll solve a couple of problems. Your favorite site won't be burdened with heavy bandwidth expenses and you have access to the image url for posting without being frustrated by broken image hot links.
http://greekgeek.squidoo.com/hotlinking
http://www.webweaver.nu/html-tips/hotlinking.shtml
http://en.m.wikipedia.org/wiki/Inline_linking