Hi Carl, I'm the lead developer for ouwiki so I can probably shed some light on your issue.
What version of the plugin and Moodle are you using? The most recent version of the plugin for your specific Moodle version should be used to ensure you have all bug fixes etc.
These can be downloaded from https://moodle.org/plugins/view.php?plugin=mod_ouwiki - note for ouwiki you should raise questions there or issues on the github project, not on this forum as it's not monitored.
If you're having problems with template images you should check they are in the template zip file (assuming the template is a zip file, if it's just xml you are using a version of the plugin that doesn't support images in templates).
Changing the reg expression near line 215 of entirewiki.php from
(i.e. removing the closing slash) seems to have solved the problem in Moodle 2.7.
For some reason img tags had closing "/" in 2.6 but not in 2.7.
Maybe this is a 2.7 bug?