Choosing whether you'd keep a physical or a picture of your receipts depends on what works best for you and your self-employed business. Here are the minimum requirements for keeping a digital copy of your receipts as per IRS:
It should be accurate.
Stored in a secure place that's easy for you to access.
Captured in their original form.
Reproducible for the IRS whenever necessary
I'd recommend consulting with a tax expert or your accountant so you'd be guided properly if you have specific questions about receipts and record-keeping. Also, you can read through these articles to help you manage your receipts in QuickBooks: