Google and Bing hijacked the ALT attribute and because of that many webmasters and SEO guru's have been using the ALT tag for rankings and not what it was originally designed for, that being impaired users or users that have images disabled in their browser (useful for people on narrowband).
Alt descriptions should consist of actual image contents and not the keywords of the page, unless the description of the image happens to naturally have a keyword appear in it.
A few examples:
- An image of Man in Suit
- Yes: A smart dressed man in a dark navy suit
A Professional Website Designer
- An plain image with the words Web Design in it
- Yes: Image with the written text Web Design
Web Design in Bournemouth
- An image of a responsive website on a mobile phone
- Yes: Example of a responsive website being displayed on a mobile phone
No: Responsive Website Design
You can find more examples on my blog post that I did earlier today, its still in draft and needs some grammar corrections but here you go.
Webmasters no longer need to fear about their keywords appearing at
the front of the alt, at the end of the alt or even not appearing at
all. Search engines can establish the contents and value of the page
with many other elements such as:
fact Google and Bing can make sense of content with little or no
markup, HTML markup just helps them understand a little easier but in
no way is it absolutely required.
Sadly, it is the year 2017 and we are still seeing SEO guides
mentioning things like the importance of keywords in Alt tags, key
word density, headers and so forth, all these things that really
mattered, no longer matter as much at all. You only need to take a
good look at Pro Webmasters, excellent rankings… which is filled with
thousands of pages with less than 90% of them having any images at all
and with hardly any HTML optimisation within the user generated
content areas of these pages.
Good usage of the ALT attribute is composing the image ALT value that
consists of a short description that informs users the context of the
image. Sometimes describing less is often more and other times more is
more! Your descriptions should contain the elements of the image that
you want them to visualise, it is not for telling Google to rank THIS
because of this KEYWORD. Treat the ALT tag as a solution for partially
impaired, completely impaired or for users that have disabled images
in their browsers.