Spiders vs. Eyes
What can the eye see that a spider cannot?
To make this simple, consider this: A search engine
spider can only read textual content, and it can only
rank your site based on what it can read. So anything
other than textual content on your web pages is merely
clutter to a spider.
With that in mind, go to any web page and look at the
HTML source instead of the way the page looks in a web
browser. Now imagine that you have never seen the actual
web page, and have to judge how well that page should
rank on a search engine strictly by what you can gather
from the source.
To a spider, an image may looks like this:
and test would look like this:
<font>Fly Fishing for the rest of us</font>
If you were a spider, which of the two would you better
The point here is to avoid using images where it is
not necessary, or at least balance images with strong
textual content. However, at minimum, when you have
an image, you can enter some alt text. For example:
Image code can read:
<img src="images/flyfishing.gif" alt="Fly
fishing for the rest of us" >
Avoid frames like the plague
Many sites use frames to make navigation easier. The
problem is that most (if not all) spiders cannot read
your frames pages. They merely see the main frames page
which calls the other pages. The content simply will
not be indexed.
Flash is great, beautiful, and often fun. But like images,
a spider will only see the call to the flash, and none
of the actual flash content. This can easily render
your website impossible to index.
PDF and DOC
Some engines can now index Adobe PDF files and Microsoft
Word documents. While we have no evidence that these
can help or hurt your ranking, at least these files
can now be indexed by some engines.