Each image taken is assigned a priority by "makefitsloop" on the Aquisition Machine before it is sent through any of the whole processing step. This priority is passed from one script to the next, never changing without intervention from the user.
The priorities are set in the priority file, which is what you give in the "priofile" parameter of "makefitsloop". The format of this file is:
title amplifier filter priority
The title is a string which is in the title of an image. Actually, it's a Perl regular expression, and this can be used to advantage if you know what you're doing. "makefitsloop" scans through the priority file. It choose last entry in that file which it finds whose title is matched anywhere within the title of the image, whose amplifier matches the image's amplifire (1-4), and whose filter matches the image's filter (e.g. R or I).
All matches are done case insensitively, so you don't have to worry about the difference between "bfc" and "BFC".
If none of the entries in the priorities file matches the title of the image, then the image is assigned a default priority of 5.
At the telescope, the operator can force the priority of an image to be different from the start. I the string "p=#" appears without spaces anywhere in the title, where # is a non-negative integer, the priority of the image will be set to that number.
This is really covered in the script setup document. However, briefly, if after the image has already been aquiried, cleaned, and compressed, you want to bump the priority of certain fields for transfer to Berkeley, carefully edit the "compressed" file (with emacs only, unless you are extremely careful not to overwrite the file if it changes after you read it into your editor). Find the entry for the image whose priority you want to change, and change the number on that line.