Hi! I am pretty sure you noticed your follow and join tumblr button in the right corner already. Beside this two buttons, you have another opportunity to support your tumblr blog outside the tumblr community.
(… It is just huge ‘cause for this post here)
This button will work in any publishing platform. Just add the button in the context next to your photography/picture.
To learn more, and to get the code for this button - take a further look at this tumblr help page > here.