how to add alt image

Hello,

I am using Twenty20 plugin in my website.

I am using this code to add images:
[twenty20 img1=”686″ img2=”687″ direction=”horizontal” offset=”0.5″ align=”right” width=”100%” before=”Antes” after=”9 meses depois” hover=”false”]

And works great.

But i need to add alt in images, how can i do it?