I added this code to the head but when I try to post something about a website inside a Facebook page, the image that I specified is still not showing up as an option. I'm using wordpress as a CMS. Any ideas why?
<meta content="something" name="title">
<meta content="something="og:description">
<link href="thumbnail.jpeg" rel="image_src">
Try using the Facebook Debugger to pin-point the issue.
Sometimes there is a caching issue and feeding your URL through this tool forces Facebook to scrape your URL again hence refreshing the cached og:tags
Further more your og:tags should look more like this :
<meta property="og:title" content="The Rock"/>
<meta property="og:type" content="movie"/>
Notice the property attribute and not the content attribute that you (possibly) used. The correct syntax is available at this link : http://ogp.me/