I have an issue when uploading images in docs.moodle.org -environment. I'm creating the Finnish Moodle-tutorial for teachers but I have problems with images that I'm trying to embed on the pages. I upload images (e.g. .png) normally using Mediawiki's upload tool. The issue rises when after the upload I get an error message saying "Error creating thumbnail: Unable to save thumbnail to destination".
For example:
1) Create an arbitrary page under docs.moodle.org/all/fi
2) Edit page so that there's a line [[Image:example.png]] or File:example.png and save the page
3) Now clicking this new file link open the Mediawiki content uploader
4) Upload example.png
5) After uploading the file the aforementioned error message is seen. The image itself is uploaded succesfully and you can find it in the uploaded files.
6) When returning to the page that's been edited instead of a new image the error message is seen.
One example of a page with broken image links can be seen here: http://docs.moodle.org/all/fi/Lis%C3%A4%C3%A4_osallistujat_kurssialueelle
According to some solutions I've found it seems that LocalSettings.php should be modified. Problem could be with file permissions.