We have realized a couple of websites with integrated facebook share / like buttons. Once a while we noticed that the facebook share dialog did not recommend any thumbnail images extracted from the current site. Digging a little bit deeper into this issue, I found out, that facebook sometimes struggles if the images on the website are specified with relative paths. Even the base href specification on the site did not help (or is simply not considered in this case).
More specific: If the current site is on level 2 or more (e.g. http://www.mydomain.com/level1/my-currentsite.html), the base href is http://www.mydomain.com/ and the image path is for example /fileadmin/news/images/myimage.jpg, the facebook share dialog might fail to extract any thumbnail images.
So how to solve this? Using an absolute url for the images supports facebook in extracting the images and producing the thumbnail recommendations.
So we have to force typo3 to produce absolute urls for the images etc. And as usual for Typo3, this is supported out of the box with a typoscript configuration (you just have to know it 😉 ):
Add the configuration:
config.absRefPrefix = http://www.mydomain.com/
in the setup of your template, clear your cache and you are done…