How do I add attachment to mandrill email plugin

I use armaldio plugin to send email:

https://www.scirra.com/forum/plugin-send-a-mail-using-mandrill-deprecated_t109399?start=60

in plugin is option to add attachment base 64

Im wondering how add attachments

for example how add canvas snapshot without download image to sending email

and/or

attach downloaded file from C2project canvas snapshot.png

any ideas how handle this?