1. A method for processing electronically presented items, comprising: receiving from a sending financial institution at a first time a plurality of electronically presented items, wherein one or more of the items received is comprised of a source sequence number generated by the sender of the electronically presented items and transaction data associated with the source sequence number; for each item received at the first time, assigning an electronic item presentment (EIP) sequence number to the item, associating the item's transaction data with the item's EIP sequence number, and associating the item's EIP sequence number with the item's source sequence number; receiving from the sending financial institution at a second time image data in a digitized format for one or more of the items received the first time, wherein the image data for each item received at the second time is associated with the item's source sequence number; for each item's image data received at the second time, assigning an image sequence number to the item's image data, associating the item's image data with the item's image sequence number and associating the item's image sequence number with the item's source sequence number to preserve a linkage integrity between the item and the item's image data; and for each item's image data received at the second time, associating the item's image sequence number with the item's EIP sequence number by matching (i) the source sequence number associated with the item's EIP sequence number received at the first time with (ii) the source sequence number associated with the item's image sequence number received at the second time, wherein the matching step is performed by an electronic item presentment computer.