Really interesting question... As a bit of a cheeky expansion here, let's say you have a product page with 8 images of a specific product. The images are all different in some way & have different file names...
Let's say you're going for the keyterm "Widget"... Is setting Alt text as "Widget 1" "Widget 2" "Widget 3"... etc, enough to separate the images from a spam point of view?
Would anyone say there is some sort of keyword density line one should not cross in relation to Alt text?
Thanks for all the replies, in response to astro, yes it is usually page furniture.
This is a scenario which often crops up.
A client makes contact who has a dreamweaver template driven site, there is one large image on each page with the alt 'attribute' set to "Widgets" but since the client had the site built they have branched out into "Sproglets" and "Doodles" Do we change the alts to reflect the subject on the Sproglets pages
The client approaches us with the same site, the same one large image and every alt attribute is different with keywords targetted to each individual page. Do we change them all to be identical?
The client want's a quick fix, and they desperately want more Sproglet sales before they go bust.
I guess my question is what will improve their rankings in Google in the short term? I'd be very interested to hear if anyone has any evidence to say that abiding strictly by the accessibility rules actually impoves rankings.
Hmmm, interesting question. I've never really thought about it. If there is a compelling reason, I don't think there is a problem using a different alt tag on the same image on different pages.
The reason is that the client needs more sales/better rankings.
So do you fix all their spammy alt attributes to achieve this.
Or in the case of a site which is using the alt attribute correctly do you override 'the very reason for the alt attributes existence' and add the extra keywords.
As others have pointed out, the alt attribute (again it's not a tag) is an accessibility attribute for screen readers... but it's also an attribute for user agents that don't support images (like text browsers or browsers w/ images turned off).
I have to disagree with most of you here. There is absolutely NOTHING wrong w/ using different alt attribute values for the same image across a given site. That makes no sense as it implies that there is only one correct description for a given image. That is like saying that link text used to link to a page should also be the same everywhere because God forbid it might "confuse" someone since there is only one description for the content of the page (NOT!)...
I agree that the various values used in multiple alt attributes for the same image should ALL describe the image itself and NOT be stuffed w/ SEO keywords. But to suggest that the search engines might somehow frown on using multiple alt attribute values for the same image on the same site is totally baseless and amusing IMO.
Google is NOT going to frown on using different alt attributes for the same image on the same site. Not every site has every page developed by the same web developer... or designed by the same web designer... so it would be totally unreasonable for the search engines to expect all of the alt attribute values to be consistant, much less actually ding a site if they are not.
Just like a picture hanging on a wall at the Metropolitan Museum of art, if you ask 100 different art critics for a 1 sentence description of a particular painting, you'll likely get 100 different answers... all very good descriptions of the same painting, but different none the less. Hell, if you asked the same art critic on 100 different days to describe the content of the same painting you'd likely get 100 different answers.
The key is making sure the alt attribute accurately descibes the image, NOT that any one description is correct. There are usually infinitely many descriptions one could come up with for the same image. It's okay to use as many as you want so long as they accurately describe the image.
Well I personally don't believe, unless it's completely clear, that google would ever penalize a site for using different keywords in alt attributes but i believe a certain trust might be built if there's clear consistency.
My above stated belief stems from the release of the google image labeler which is promoted as something we can do to "help improve the quality of Google's image search results".
So there is a possibility that the less 'confusion' that is created the easier it will be to read your site and that might be where the benefit comes in - i my head anyways.
Bear in mind that not all images require a description, and in many cases it is not desired, owing to the excessive verbosity that can result which will tend to muddy the waters rather than clarify. Stand back a moment and take in the whole page, attributes and content combined and just listen to it. If it sounds confusing, it is.