Agree with Paul here.

A 301 is a directive to the crawler, while a canonical tag is only a hint and is not always followed. Bing for one will ignore canonical tags if it believes they are misused.

as for the mention of "multiple 301 redirect" .

You do not need to have a 301 redirect for every url, just follow the logic
if HTTP_Host is not myPreferredDomain then redirect to myPreferredDomain

Could very well be,

Google has stated that they penalized m,any sites because the wrongly thought they were parked

http://searchengineland.com/dropped-in-rankings-google-mistake-over-parked-domains-118979?utm_source=feedburner&utm_medium=feed&utm_campaign=feed-main

Yes 500 errors will affect ranking, SE like a site that is well mainated, obviosly they dont want to send users to a error page.

Can we get a url, I will take a look, and may be able to advice you.

Yannick seems to have it right, but here is another way

<system.webserver><rewrite><rules><rule name="DefaultRule" stopprocessing="true"><match url="^index.php"><action type="Redirect" url="/"  =""></action></match></rule></rules></rewrite></system.webserver>

Dont use no-follow, you will just leak link juice.

One way around this, is to use a anchor # in your url for the image. like page.html#someterm

This will in fact give you link text relevancy for both, google will see this as 2 different pages.

Make sure you have alt text for the image.

This tataic and well as what x-com may in the future be seen as over optimization, so it may be tter to do somthing like this

Your link text

You can just link the whole lot in the one link.

Or move your text to above the image.

I should not of said 2 pages, but it has been shown that both links will give link text relevancy.

The javascript link will be followed, it will not help