These are not "New" images and it is Class 1 objects, not Class 3 that are of most interest.
From ATSB
MH370: Sonar Contacts Fact Sheet - 29 July 2015:
There are three classifications for sonar contacts which are identified during the course of the underwater search.
Classification 3 is assigned to sonar contacts that are of some interest as they stand out from their surroundings but have low probability of being significant to the search. The underwater search so far has identified more than 400 seabed features that have been classified as category 3.