Symptoms

After clicking on an image thumbnail, Confluence shows a continuously spinning loading icon as shown below:

Cause

There are a few possibilities which might lead to this problem occurring:

1. The Gallery Plugin is causing conflicts with the built-in functionality.
2. The Server Base URL is set to a different value than the URL you are using to access confluence. There is a bug filed for this issue:

CONF-7692 - Getting issue details... STATUS

Resolution

• If the instance has the Gallery plugin, uninstall the Gallery plugin via Administration Console >> Plugins. This will not disable the functionality provided by the Gallery Plugin since Confluence has a bundled {gallery} macro (it's part of the Advanced Macros plugin).
• Configure the Server Base URL via Administration Console >> General Configuration >> Site Configuration >> Server Base Url to be the same as the URL you use to access confluence. If you cannot do this, please see the workaround below:

Workaround

This is a workaround for users that cannot set their Base URL to be the same URL as the one they use to access confluence.

Try the gallery macro. If you are want to show a single image in the gallery macro you can try the include parameter as shown below:

{gallery:include=<image file name>}

Change the <image file name> to the fit your environment.