Recently two of my friends, Ram from Teknobites and Kanak from Tecfre had problems with their posts getting copied by other blogs. The blog has copied the content word by word and also linked the images directly with the original blog. Stealing content and images is actually a very serious problem and there are many ways to tackle them.
I did a search on how to protect hotlinking of images from your blogs and found this plugin- HotLink Protection for WordPress blogs. Although its possible to set rules in .htaccess and enable hotlinking protection, for normal WordPress users these may be complicated.
This plugin is very simple to use. Upload the plugin and activate it in Plugins. In the options tab, you set the path of the file for which hotlink protection is required.
If anyone link your image directly, then it will show up a default image provided in the plugin. You can also add a custom image for protection. The best thing is that it does not block the images in the feeds.
NB: Although the author says that this plugin will not break feeds images, there are chances that it images may not show properly in some feed readers.
You can download this plugin from the here.