We use Ledger for all of our accounting (it's not too much... yet) and we've been using comments in Ledger to keep track of our receipts.

Example:

    2015/02/05 Clipper Card
        Expenses:Transport:Public Transportation               $20
        Liabilities:Reimbursement:Zach Latta
        ; Receipt: 52fae6a40afaf2a79bfdef92f5e1b6d3.pdf

Each receipt filename is <md5 hash>.<extension> and they're all tracked in a private GitHub repository.

Here's a link to our repo with more examples: https://github.com/hackedu/finances/blob/master/main.ledger