Don't know for sure in your case but usually the mfgr. info is on the breaker side. Take a look at the main breaker and the sub circuit breakers and if they are all the same mfgr. then the breaker is likely original.
I see 4 mounting holes in the face plate. DO they match the mounting holes in the breaker face. If they do then the breaker is likely original.
A different breaker mfgr. would likely have used a different screw pattern.
The switch on my boat has an adapter plate to mount the breaker.
If you are looking to replace the breaker, get the name and numbers off
the breaker and check online. Did a search some time ago and found it.
Didn't need one at that time so I didn't save the info.
Thanks folks. The manufactures are different for the Main & sub breakers. Oddly, the main breaker mounting holes are same spacing as those in the panel but the breaker is too small to screw right into them or fill the gap by itself.
I turned it sideways and lodged it in the space and think I will use Milt's suggestion and make an adapter plate to tidy up the panel