No, that won't work because images, as well as any html or php file needs to be within the root of your site.
I think you should look in to the Mod_Rewrite apache module. You could do something like this in your .htaccess file(s):
RewriteEngine on
RewriteCond %{HTTP_REFERER} !Your-site.com
RewriteRule /$ /images/you-cant-view-this-image.gif
I acually tested this, and it doesn't work (so dont use this code), but you should be able to get it working if you spend some time on it.
I've only used Mod_Rewrite once before, but it is very useful if you know what you're doing.