Symptoms
When you set the property on a form to anonymous access, and then use the file / image attachment on a form.
Where you load a file towards the image attachment control then the image won't display / work. It seems that the file.ashx retrieval gives an access denied (via fiddler).
Diagnoses
For this to work we have to add a configuration to the web.config file of the Anonymous Runtime site.
Resolution
A configuration setting should specify whether user is allowed to download (or load) files while accessing control through Anonymous access.
The configuration setting in the web.config is the following:
Configuration should be set to true to allow attachment control to function correctly while accessing through Anonymous access.