This question already has an answer here:
When I share images with the folks in The Nineteenth Byte, I frequently find myself double posting just so that I can explain what the image is about or why I bothered posting it. For example:
Addind any text other than the link prevents it from being oneboxed. That means that if I have to post the image alone. If someone finds it interesting and stars it, an ugly imgur link gets added to the transcript. Others have to click on it to have a clue what it is about.
In addition to the current oneboxing...
If the entire message consists of
[MESSAGE](LINK) and that link is otherwise oneboxable, just onebox it and display the message above it. For example, the following message would show an image of the weather with "Hello, cold, rainy world!" floating above it.
[Hello, cold, rainy world!](http://i.stack.imgur.com/jYXpI.png)