Full Idea
An image cannot constitute a memory, because we notice that the image is in the present, whereas what is remembered is known to be in the past.
Gist of Idea
Images are not memory, because they are present, and memories are of the past
Source
Bertrand Russell (Problems of Philosophy [1912], Ch.11)
Book Reference
Russell,Bertrand: 'The Problems of Philosophy' [OUP 1995], p.66
A Reaction
This sounds a bit glib, and maybe makes the mistake for which he criticises Berkeley, of confusing a thought and its content. The puzzle is how we know that some images represent the past, others the present, others predictions, and others fantasy.