Following is the code I am using to share my posts on Facebook. Everything is working properly but sometimes on some posts the thumbnail image is not showing.
<?php
$title=urlencode('Facebook Share Platform');
$image=urlencode('imagepath');
$summary=urlencode('Check This Out');
$url=urlencode('http://apps.facebook.com/yourapplication');
?>
window.open('http://www.facebook.com/sharer.php?s=100&p[title]=<?php echo $title; ?>&p[summary]=<?php echo $summary; ?>&p[url]=<?php echo $url; ?>&p[images][0]=<?php echo $imagepath; ?>', 'sharer', 'toolbar=0,status=0,width=626,height=436');
I have checked the URLs and everything I could but couldn’t figure out the problem.
Is your image at least 50×50 and with an aspect ratio of 3:1 or less?
You haven’t really given enough information there to solve your issue, so I’m just guessing based on the most common issue i see
{edit:}
The 3:1 image ratio requirement is documented here and appears to be the OP’s problem