JacFSB
As a financial crime detective in CA in the 1980's, I ran into this problem frequently because original items were lost or misplaced. We lost or misplaced them, too. Imaging technology was in a state of infancy and most institutions didn't image items as they do now. Because imaging was a relatively new technology, getting a court to admit an image of a document instead of the original one was difficult. No longer -- and Mary Beth may want to add to this thread because it can get complicated.
Generally, a copy of an original document may be admitted into evidence if it is shown that it is a true and correct copy of the original -- and the original is unavailable. The document must have been legally acquired in the course of normal business and it can only be admitted by the witness who was involved in the transaction -- or by the institution's designated custodian of records. No copy of an original document may be used for handwriting or fingerprint comparison or identification purposes.
In my experience, a photocopy of an original document is more difficult to get admitted in many instances than an imaged one. Most courts have acknowledged that an imaged document is the "next best evidence" if the original is unavailable -- so check with your local jurisdiction for its admissibility guidelines.