can i use back camera capture several photo when field check-in?
No. Why do you need to do so?
We need back camera check-in to collect more data from employees. It will improve employees efficiency.
I think you may have misunderstood the purpose of Field Check-In.
This feature is to allow employee to provide proof of presence at a place outside of office.
If you allow back camera, you will not be taking employee selfie. In that case, it will defeat the original purpose.
If you need your employee to upload certain photos, you may ask them to take those photos, then use either Document Sharing, or use Document Workflow or even Discussion to upload.