Is there a way to extract rosbag files without using ros packages

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You could see whether swri-robotics/bag-reader-java has some useful parts.

I must agree with @ahendrix though: in general bags are really only fully useful with ROS in the mix, but for just extracting image data you should be able to get by with the implementation I linked above. Note that this will just get you the data. Decoding it will be on you.

Edit: opinionated bits below, feel free to ignore.

While ROS is useful, t's very annoying to install.

This is rather subjective, but I have a bit of a hard time agreeing with this (especially the very part). ros-core is less than 50 MB iirc (total size of pkgs) and has a relatively limited set of dependencies. The Docker images are between 290 and 390 MB, which is also rather small. A from-sources install on a regular Ubuntu or Debian desktop is also trivial (5 lines and some time).

I'm trying to make an extraction pipeline that is user friendly and can be used across multiple platforms and ros packages just get in the way.

One accepted approach I've seen used is to delegate the ROS/platform specific parts to a hosted web service, which takes care of massaging the data into whatever format you like. Several platforms/companies have formed around this idea, such as Bag Database, Marv and BotBags. Using a REST API the format specifics can be delegated to the hosted services and clients can download whatever formats the server can transform the data into.

A disadvantage of this approach is of course that clients would have to upload their bags first.