Facebook Open Graph og:image exists but is invisible - facebook

Question

I'm using the Open Graph Object Debugger to test this link: http://ayconatest.co.nf/?p=1957, and all the properties are there including the image, except it's invisible. You can click on it and see it, but it doesn't show up, even though the dimensions are 500x375 px. What's up with that?
Here's my header code:
<?php if (have_posts()):while(have_posts()):the_post(); endwhile; endif;?>
<!-- the default values -->
<meta property="fb:app_id" content="271801723026128" />
<meta property="fb:admins" content="779283165" />
<!-- if page is content page -->
<?php if (is_single()) { ?>
<meta property="og:url" content="<?php the_permalink() ?>"/>
<meta property="og:title" content="<?php single_post_title(''); ?>" />
<meta property="og:description" content="<?php echo strip_tags(get_the_excerpt($post->ID)); ?>" />
<meta property="og:type" content="article" />
<meta property="og:image" content="<?php $src = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), array( 500,375 ) ); echo $src[0]; ?>" />
<!-- if page is others -->
<?php } else { ?>
<meta property="og:site_name" content="<?php bloginfo('name'); ?>" />
<meta property="og:description" content="<?php bloginfo('description'); ?>" />
<meta property="og:type" content="website" />
<meta property="og:image" content="http://ayconatest.co.nf/wp-content/themes/imbalance2/images/logo.png" /> <?php } ?>
And here's what it returns (Ctrl + U):
<!-- the default values -->
<meta property="fb:app_id" content="271801723026128" />
<meta property="fb:admins" content="779283165" />
<!-- if page is content page -->
<meta property="og:url" content="http://ayconatest.co.nf/?p=1957"/>
<meta property="og:title" content="النباتات تستطيع القيام بعمليات GoPro لاقتصاد الطاقة" />
<meta property="og:description" content="كلما أثيرت مسألة للنقاش في الساحة الوطنية حول ما يتصل بالهوية الحضارية للشعب المغربي إلا ووجدت تيارين متقابلين يتجاذبان الموضوع ويعبران عن رؤيتين متضادتين, أو مايصطلح عليه Statu-quo وهذا أمر طبيعي، وطبيعي كذلك أن يكون أحد الرأيين وأحدهما فقط صائبا ما" />
<meta property="og:type" content="article" />
<meta property="og:image" content="http://ayconatest.co.nf/wp-content/uploads/2013/06/plantsthumb.jpg" />
<!-- if page is others -->
Incidentally, the debugger detects and shows any other picture that is hotlinked from another website. This leads me to think there's something wrong with my hosting, or maybe my folder structure? but I don't know what exactly.

Answer 1

The URLs used as the og:image in your examples doesn't exist / work:
I checked them both - and the screenshot below is of what happens when I try to reach the second example, http://ayconatest.co.nf/wp-content/uploads/2013/06/plantsthumb.jpg
Ensure the value you set for og:image is accessible externally and that should fix your issue