Duplicate Content Errors new website. How do you know which page to put the rel canonical tag on?

[artscube.biz]

I am having problems with duplicate content. This is a new website and all the pages have the same page and domain rank, the following is an example of the homepage. How do you know which page to use the canonical tag on?

http://medresourcesupply.com/index.php

http://medresourcesupply.com/

Would this be the correct way to use this?

Here is another example where Moz says these are duplicates. I can't figure out why because they have different url's and content.

http://medresourcesupply.com/clutching_at_the_throat

http://medresourcesupply.com/index.php?src=gendocs&ref=detailed_specfications &category=Main

[artscube.biz]

Thanks for the response Ruth, that was very helpful.

[RuthBurrReedy]

It looks like for that second link, there is no text content on the page - only one big image with the specifications of the item. That brings the unique text content on the page down to almost 0. The picture of the man clutching his throat is also just a page with one image on it, and no text. Since neither the Moz Crawl Test tool nor Googlebot can see pictures, they are left with the impression that these pages are almost identical.

It's important to remember that the canonical tag is only one way to address duplicate content concerns - "duplicate content" doesn't always mean "canonical tag." Sometimes, when pages have very little content, they appear to be identical or near-identical even if their intents are different. In that case, I recommend seeing what you could do to make the pages more unique. With image pages, I wouldn't worry too much about adding content, but for pages like http://medresourcesupply.com/index.php?src=gendocs&ref=detailed_specfications &category=Main, where there is content, but it's contained within an image, I would recommend recreating the text contained in that image, but in HTML text. You could also expand upon the specs to make them more detailed, which will add to the unique content of the page and help users figure out if this is the item they really want.

[artscube.biz]

Thanks for the response. So I would want to put the canonical tag on all other versions of the homepage except the /index.php one?

"for e.g., this page

http://medresourcesupply.com/index.php?src=gendocs&ref=detailed_specfications &category=Main

should have this rel canonical tag

"

The first link is a different page from the homepage. Why would I want to place the canonical tag for the hompage on this one?