Recently I came across an Image Library on a SharePoint 2010 farm where the thumbnails were visible but opening the images threw a correlation ID. The error message behind the ID was a System.Runtime.InteropServices.COMException which is an ACL related issue. The library inherited permissions from its parent so to solve this issue I broke inheritance and re-established inheritance again. When I re-established inheritance the system refreshed the ACL from the parent and fixed the issue.