Errors found while checking this document as HTML5

Hi All,

I used W3c to validate my website, but it popped up with a number of errors, which has baffled me.

I have 20 of these, but Im not sure how to fix them: heres an example below:

Line 581, Column 273: An img element must have an alt attribute, except under certain conditions. For details, consult guidance on providing text alternatives for images.
…ww.bournemouth.com/wp-content/uploads/2012/09/Classic-Autumn-Leaves.jpg” />

I have alternative text for these, so Im not sure how to fix them, any ideas please?

Many thanks

Rob