Does a link need text to count towards search engine rankings? I realise that there are many ways to link: - Linking Text - Linking an Image - Deceptive hidden links (Bad and black hat normally, I know) Would the search engines take any notice of links to my website that were just empty tags; for example <a href="http://www.example.com"></a>, or just a single character like a dot (.) or underscore (_)?
your upper two options(Linking Text, Linking an Image) are good, but last one comes under blackhat seo.
text links are most effective with keywords used as the anchor text. so yes it does matter. if an image is used, the it should have the title and alt tags to describe the link. don't use a single dot or an underscore. that's just as bad as deceptive hidden black hat links.
The problem with just using a . or _ is you are not giving that link a real anchor text. Technically no you do not need to have relevant anchor text, you could just put any character there. However to get the full benefit of that link, I suggest using a keyword or keyword phrase that points back to the site you are linking to.
For years, I used a link around my copyright notice tied to my copyright info page. I had no problem. Then someone brought it up to Google, and I wen from a PR6 to3. Single character link are easy to detect by the SEs. As for your statement, any link is good but will G count them. No link text - no. Image links - no. They do not show up in WMT external links. Single Char links - no. Hidden text. G will bust you. Two Char links - unknown Three Char - Yes - They show up in my WMT external links ("SEO") More Char - Yes What is still up for debate is the <noscript> link < noscript> <a href="http://www.salonateatoncourt.net/" title="Salon at Eaton Court">Salon at Eaton Court</a> </ noscript> Although this is a SEOed, HTML legal command, G will bust you for it when someone rats you out. Otherwise, they let it go and WMT External links show them.
IMO, for identifying a page SE bots only need the URL. But when it associates with descriptive text, they get a better understanding on page's content. So, if you use images, add a relevant descriptions to "alt" attribute and "title" attribute of link, Ex: <a href="http://www.example.com/cooking-recipes.html title="Cooking Recipes"><img src="....." alt="Cooking Recipes"></a>