Question

I’ve read that <img></img> (is illegal);
I’ve read that /> is optional and it’s only there for “transitional policies”.

Can this be a correct syntax for img element?

<img src="/somepath" alt="required foo">

I’m asking this because Netbeans 7.0.1 detects that has an error and made me wondering.
It does the same for other void elements like: <br>

Answer 1

It would be a correct syntax if src wasn’t empty!

As the question has been edited, yes, it’s a correct syntax for HTML5.

EDIT: but you can explicitly close your element too

http://dev.w3.org/html5/html-author/#elements

In XHTML, the XML syntactic requirements dictate that this must be made explicit using either an explicit end tag, as above, or the empty element syntax. This is achieved by inserting a slash at the end of the start tag immediately before the right angle bracket.
[…]
Authors may optionally choose to use this same syntax for void elements in the HTML syntax as well.