provenance of images displayed during a behavior session

[matchings]

Currently the images that are displayed in a behavior session are not saved and recorded in the output pkl file, or another stable location. This could be done via an asset server, or the images themselves could be stored in the pkl file directly, as was done previously in development code. This is probably a Technology and/or MPE issue, but is being documented here so that it is not forgotten.

[rhytnen]

Thanks @matchings

I am mulling over some options here and @nicain informed of some possible services coming online soon that might be appropriate for this.