Which is better in links from the search engines' point of view: plain text or images with an alt attribute that says the same thing? For example, is <a href="">This is a link</a> better than <a href=""><img alt="This is a link" src=""></a>?
SEOs I've spoken to before about the subject claim that all links to important sections of your site should be plain text rather than image links. Which means that if you want to give links a particular graphical look that can't be achieved with plain text, your only other option is to use an image replacement method.
But I wasn't convinced that search engines (Google at least) viewed the two examples that much differently, so when Maile Ohye, Developer Programs Tech Lead at Google, wrote a post at the Webmaster Central Blog about the Importance of Link Architecture, it gave me the opportunity to ask this very question. Her response was:
We're pretty capable of detecting image links for crawling purposes. Accurate, not spammy, alt text is beneficial in many ways -- it's helpful to users, not just as a signal to search engines. If you have useful image links (or even just for images) it's good to make the alt text descriptive.
Tyssen, if your image links are formatted similar to your example, you should be fine. 😊
So it would seem that images of text in links with alt attributes that describe the text is no worse than links that contain that actual plain text as far as Google is concerned. Which also means that image replacement may not be necessary in most situations as the text is still in the page and readable by machines (and people with images turned off).
This is of course just one person's viewpoint (albeit the view of someone who is better placed than most to comment on the issue), so I'd be interested to hear from others if they have any evidence that either backs up or refutes this assumption, and also whether the other search engines have a different take on it from Google.