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Thanks Vinnie, I've just done some investigation on Seripiq.com and its been really useful.

key-phrase.example.com Anytime, you can get your keywords in the URL of your image, the better it will do for rankings. But do realize that subdomains do not boost your main domain's rankings like a sub-folder would. But I suppose this all depends on what the end goal of having your images rank is.

Internal link certainly does affect ranking like every other link. http://perthseocompany.com.au/seo/tutorials/a-simple-explanation-of-pagerank

Is there a difference between , and font-weight: bold, in terms of SEO weighting? ****Each search engine is a private company and can choose to weigh things as they see fit. I can share for Google those factors are treated identically. It is likely other search engines treat them the same but I cannot confirm that information. Does font size make a diffence, relative to the average font size of the page? The historic best method to adjust font-size was the use of header tags (h1, h2....h6). This method affects font size and is weighted by Google. If you attempt to manipulate search results by changing font-size (such as font size = 1) then that certainly can impact SEO with a penalty. Google is definitely aware of relative font-size and it likely is a ranking factor. I have seen numerous indications of such, but am not aware of any 100% conclusive statement to that effect.****