App or tool for auto-crop receipt-like pictures?

I've bunch of scan of [receipts](https://en.wikipedia.org/wiki/Receipt) , the one that are printed on [thermal paper](https://en.wikipedia.org/wiki/Thermal_paper) which you get from any supermarkets and these were taken on the dark background. I'd like to auto-crop them in batch via some tool, to not include the background. I'm looking for app or tool for batch auto-crop of receipt-like pictures taken either for iOSX or OSX.