Trying to get property 'post_title' of non-object with

Seems like your $value variable is not an instance of WP_Post.

If your code is inside the WP loop or in a single post or page, you can use get_the_title() instead of $value->post_title.

Else, you have to set the variable with the post, like this:

<?php $value = get_post(100); // change '100' with the right post ID ?>
<a href="'. (!$is_placeholder?$image[0]:'javascript:void(0);') . '" ' . (!$is_placeholder?' rel="prettyPhoto"':'') . '><img src="'. $image[0] . '" title="' . $value->post_title . '" style="height:80px;width:80px;"/></a>