Behaviour with required fields

Problem/Motivation

If we have Alt text or Title required for such image fields, and try to submit,
it should identify someway that alternative text or title is required. Now it shows nothing, and it's a bit uncomfortable for editors

Steps to reproduce

Add field_image with title/alt required, use Nice Imagefield widget,
try to add some images and submit

Proposed resolution

Add some error text to inform user that some images alt/title are not filled