How do I indicate origin and accuracy of new location coordinates?

If coordinates are sourced directly from another publication, this should be clearly indicated by adding a reference on the "location" resource. To indicate the horizontal accuracy (when known) or in cases where coordinates have been derived through analysis of maps or spatial imagery, Pleiades uses a special document called an "accuracy assessment".

There are already stock imagery assessment documents in the Pleiades system that can be re-used when appropriate. When you determine coordinates through analysis of imagery in Google Earth. Just search for "google" when trying to link to an accuracy assessment and choose the one containing the most recent year matching the imagery date you're using. There are also stock accuracy assessments for GeoNames, OpenStreetMap, generic hand-held GPS units (if you've collected the coordinates on-site yourself), and more.

To view a short video demonstrating how to add an existing imagery assessment document to a location resource, see http://youtu.be/g-H6Tn87hyc.