What's the smallest OS that could be put into a pendrive to boot a MacBook Pro?

The question, obviously, refers to Linux OS's only but if there's something besides that it might proof helpful at the end.

The problem I've is that in its hd there're hundreds of photos that the owner want back. The machine is just showing up a folder at the center of the screen with a '?' in its center. The screen itself is showing a collage of rectangular forms forming something like a mesh or filtering net.

The RAM appears 'OK' but I've not opened the laptop yet, so I'm not sure that I can attest as to the proper coections of the hdd nor if it is even spiing at startup.

What about "unetbootin" or something like that? it has a cd/dvd rom unit that appears to be working.

At the end, what I need is first: to disce if it can boot irrespective of OS or capabilities of it; second: if I can access the hdd to find the desired info for saving it to an exteal media; third: if the info is accessible then it might be useful to have inteet capabilities for sending that info to the cloud.

Thanks in advance for any kind help on the above!