The images are LORRI images; however, because of bandwidth constraints (about 1000bps), these are lower-resolution versions of the LORRI images for press and initial science work. e.g. a one-tenth-resolution image takes about 3 hours to download. See here for a description of the sequence of transmissions:

https://youtu.be/ymJRlUQfPfQ?t=586

EDIT: The full download of the gigabytes of data from the flyby will take 20 months to download.

Emily Lakdawalla wrote a great timeline here. http://www.planetary.org/blogs/emily-lakdawalla/2018/what-to...

The best shots won't be for a while, but hopefully the team received some informative images today or tonight and will be able to share them at tomorrow's press conference. As she notes, there is a chance that the first downloads will miss Ultima Thule entirely. The encounter was just that difficult.

As for LORRI and Ralph, can't we call them both "primary?" Only Ralph produces color images, so most color shots of Pluto are Ralph's (https://solarsystem.nasa.gov/resources/639/the-frozen-canyon...).

LORRI has higher resolution, which is why some of the most stunning shots of Pluto are black and white (https://solarsystem.nasa.gov/resources/652/plutos-majestic-m...).

Some images were produced by "painting" Ralph's colors onto LORRI's high resolution features (https://solarsystem.nasa.gov/resources/699/pluto-dazzles-in-...).