All memories must contain some form of the phenomena of imagination as it would be impossible to remember an event exactly how it occured. You can broadly express how an event may have occured but more imagination is required the more granular you are willing to go due to how the relevant components of the event moved within the timeframe the event occured.
What we can express more concretely, are memories which are backed up with evidence beyond a reasonable doubt and aren't just circumstantial imaginations disguised as memories.
for example, i have a memory of the Chicago Bulls beating The Lakers; immediately after the game i am able to recall who scored at various points in the game with my friends who also agree on the sequence of events which took place. We then go home and rewatch the game on television and various spectators recordings on YouTube - this public record of history reinforces the memories i recalled immediately after the game before rewatching them.
Despite this, my memories immediately after the game contained some imaginary elements due to the fact i could not recall the event on a timestamped granular level, however my broad memories of the game were correct as they actually happened.

Could we have a robust legal system whereby witnesses were required if memories were indistiguinshable from imaginations? possibly not, but indubitable evidence would possibly plug the difference...