First things first, make sure the following permission is obtained:
publish_stream
Now, assuming you have created a $facebook object using the SDK, you can then post to the stream including a picture on the lefthand side:
$attachment = array
(
'access_token'=>$facebook->getAccessToken(),
'message' => 'This is the message',
'name' => 'NAME',
'caption' => 'This is my caption:',
'description' => 'This is the description',
'picture' => 'http://www.facebookanswers.co.uk/img/misc/iq.jpg'
);
$result = $facebook->api($this->id.'/feed/','post',$attachment);
The message field can be omitted if you want. I have included it so that at least you know it is there.
You need to change the contents of the fields to suit your needs, but hopefully you get the picture.