If images in detail view or the original images in pop ups aren't displayed this will be mostly caused by one or more certain system plugins.
It's pretty easy to check whether that's actually the case by disabling all system plugins in the plugin manager of Joomla and checking whether the images are displayed correctly after that. This is possible by filtering for 'system' first. Please note that it is very important to leave solely 'System - SEF' enabled (in order to not disable the SEF functionality).
If you are able to see the images in frontent after this step this is the proof that one of the installed system plugins is responsible for the problem.
Now you are able to find this plugin by enabling the system plugins again step by step while constantly checking whether the images are disappearing after a refresh of the page.
If you have find one or more such plugins please verify at first whether you site needs this plugin absolutely. In this case please report this with the name of the plugin in our forum and we may be able to help.
Additionally you could be able to help others by searching the plugin in the following list (it isn't complete). If it isn't there yet please report that in our forum, too. Thank you very much!
Is one of these plugins wrongly on this list (due to e.g. a bug fix release) or are you a developer of one of these and have some questions about this problem please don't hesitate and write us a mail.