Let us do or die.
The source for the proverb is Forty Thousand Quotations: Prose and Poetical by Charles Noel Douglas (Bartleby.com). The poster is made with AutoMotivator. Douglas attributes this to "Campbell," but I know the words from Robert Burns' Scots Wha Hae which you can read at Wikipedia. The image is by Art History Images (Holly Hayes) at Flickr showing the statue of King Robert the Bruce in the forecourt of Stirling Castle.