On OSX/Linux you can try with ImageMagick command-line tools (e.g. Trimming 'Noisy' Images -- Scanned Images).
Alternatively you can try Scan Tailor (at GitHub), an interactive post-processing tool for scanned pages (installation via Homebrew: brew install scantailor). Convert the images either from ScanTailor's GUI interface or from the command-line (Run:
scantailor --help for help).
Check similar Q&A for Windows/Linux: Auto-crop black margins dynamically of scanned images?
For iOSX app (also available for OSX), you can try Evernote, so you can take a picture of documents or business cards (including OCR), and the app can auto-crop it (based on the content).
Other apps include: Receipt Bank, Expentory, Xpenditure, Kagazz.