Picture element with different image formats

gistfile1.html

<picture alt="Alt tag describing the image represented"> 
    <source src="photo.webp" type="image/webp"/>
    <source src="photo.mng" type="image/mng"/>
    <source src="photo.svg" type="image/svg+xml"/> 
    <img src="photo-s.jpg" /> 
</picture>

// Notes
//----------------------------------------------------------------
If browser supported the webp image format it would use that image, 
otherwise use the next image format in the source order. If the browser 
does not support any of the image formats in the source elements, it would
default back to using the img element.