As I always say hotlink the images from the websites which allow you or those websites which are only created for upload and hotlink purpose.
Well there is a reason behind that.
Not every but most of the websites get a limited transfer limit or bandwidth or usage limit.
Now actually what is bandwidth? The answer is simple as human has stamina of working there is same thing with website. Website has some limited stamina of data sharing/transfering. For example a website gets 1000 GB per month transfer limit. Now when you view the picture of 100 kb, the amount of data u downloaded in temp memory (i.e 100 kb) is deducted from the website's bandwidth. This process continues, we download, view the data and if the bandwidth limit is out within that month the website will be unavailable to visitor. Lets come to our topic if we are hotlinking the image we are stealing their bandwidth, it is same thing u r using ur friend's car for ur purpose and using his fuel.
How Can I prevent that?
Simple Go to http://www.imageshack.us
click the radio button URL and paste the image link, the image will be transfered to imageshack server and this method is fast as compare to downloading the image and uploading it to image. Because you are transfering server to server (internet to internet).
Am I stealing the imageshack bandwidth?
Yes, but they allow this, because they have a very large limit of bandwidth (unlimited) and this website is for image hosting and hotlinking purpose. So u need not to feel guilty in hotlinking from imageshack.
Articles & Other Informational Stuff
We are not allowed here to give the direct url of the websites, but yes as per ethics you can give the name of the person who wrote the article or if unavailable you can mention source in organization name suppose if you are taking article from bbc.com you can give source as BBC.