Full paths to images

I’ve installed WordPress and followed the guide “Giving WordPress its own directory”.
It seems to work perfectly.
Now I have the Index and .htaccess on root and WP has it’s own folder.
I have a question thought.
When adding images, why do I have to write the full path:
<img src=”blog/wp-content/themes/Mytheme/images/image.gif” alt=”image” />
I’ve seen people just including “images/image.gif” but it doesen’t seem to work for me.
Is there any trick I’m missing ?

Thanks a lot.