Repost for Instagram makes it easy to #Repost your favorite photos & videos on Instagram while giving credit to the original Instagramer.

When you find something you want to repost in Instagram, simply copy the share URL and open Repost. Then in Repost, you can position the attribution mark and send the reposted media back to Instagram.

NOTE: This app requires an Instagram account to use (sort of).
From version Repost for Instagram 3.2.2:
Fresh bug fixes.
All versions