try this
(not my work)
Most of the images have a common username root
The default password for the other images are generally as follows;
Username = root
Password for Beta image = BLANK (AS IN NOTHING)
Password for DS image = dsteam
Password for juliet = technomate
Password for UR5/6 = admin
Password for UKUR = BLANK (AS IN NOTHING)
Password for EDG = BLANK (AS IN NOTHING)