the reason why you're seeing a question mark is because the link to the picture isn't properly set.
Since you've figured the way to upload a picture to your server AND to include the necessary code in your posts, you don't need a plugin.
Unless you're willing to do that very often, then the plugin might save you some time.
Now, the best thing would be to solve your bad linking.
Can you provide us either with the incriminated source code and/or a link so that we could troubleshoot that ?
You're linking to a website where I haven't seen any wordpress install so far...