1) Your download products are not marked as taxable.
Edit the products in the product base (Photo Products -> Product Base) and be sure the taxable option is checked.
2) Only downloads are being purchased and you don't have the state field enabled for "Download Only Orders".
Settings -> Account Requirements. State (and Country for VAT) must be selected in order for tax to be calculated. So if someone is only ordering downloads and Download Only Orders is not checked for state, then it has nothing to calculate tax on.
