Like I said, I do agree with you. I just realised, you are correct about Google using the alt attribute for image searches.
I was just against the use of "SEO" as a reason for adding the alt attribute for images.
The biggest problem would be that changing such behaviour would break BBCode compatibility with boards that use the "standard" BBCode. However, I do think the pros outweigh the cons. I'm sure it would be possible in a conversion to change the BBCode structure as well.
I believe it has been discussed before, but the best way to implement would probably be the following change:
Instead of
Code: Select all
[img]http://www.example.com/image.png[/img]
use
Code: Select all
[img=http://www.example.com/image.png]Alternative Text[/img]