Adding custom images on SharePoint Addins

Hi All,

I am developing a custom add in on SharePoint Online and created acustom action on the ribbon control.
I need add some images inside the Visual Studio 2015 and create a new folder namesCustomImages.

However, instead of  adding default images,   
Image32by32="_layouts/15/images/32by32.png"
Image16by16="_layouts/15/images/16by16.png”

I would like to add images like
Image32by32="/_layouts/15/images/Custom32by32.png"
Image16by16="/_layouts/15/images/Custom 16by16.png"

But after deploying the add in, I got red icon for image not found.

I uploaded images to SiteAssets and references images as
Image32by32="/SiteAssets/32by32.png"
Image16by16="/SiteAssets/16by16.png"

But result is the same.

Q: How could I reference custom images on SharePoint Add ins?
Q: Do we have token for Site Assets?

Any help would be appreciated.
Thanks.    

Sandy