Preview is not showing after upload
Could be that you have private file setting turned on and have not given permission to authenticated users to see an uploaded field.

But the commenters above are correct, there are literally a dozen or more ways a field may not display an image. A few that come to mind:


Images styles aren't writeable
A preprocess function has a weird permission it's checking
.htaccess or server settings is screwing up the image headers
the path is getting rewritten because of a path alias
Some access module is being wonky
The access permissions are out of date and need to be flushed
You have a field-level access module preventing authenticated users from seeing the image field
You are using some display module that is tweaking your template or display mode based on permissions
The views module is tweaking your field availability
etc