If you do not want to require your employees to upload an image specifically for mileage, you can update your submission policy for mileage reimbursements.
Head right here to update your submission policy. You'll be able to update your submission policy for both mileage and regular reimbursements:
From there, click the edit icon for mileage policy. From there, update the policy according to what you'd like for your team and then click "Save Changes". You should then be all set!