Hi,
At ecc where it stores am not sure. But changed record history will be stored at tables CDPOS and CDHDR
But based on delta type we can check those images at DSO.
Delta type you can check for your data source at RSA2 or use table ROOSOURCE. There will be a field Delta type - ABR,AIE,ADD ...etc.
On google please search about "0recordmode and delta type concepts in bw".
It might be helpful.
Thanks