So, the old camera is not supported?

Let's see what we can do...

You can imagine to work on a driver for it, you said?

But will it be worth it to do that work?

Currently, we do not know what the work will be to get a driver for the camera.

It may be insanely difficult, or pretty easy - let's jump into our example to get a better overview:

You were looking at the right place with gphoto2.

That is the place to look whether the camera is supported;

gphoto2 is not only that command line software you know,
it contains also the drivers that is used by it; It's a big package of drivers and tools that go together.

So even if we want to develop a new driver, we are in the right place. And in both cases, we need to dig through any information that may be relevant.

Now, let's look for the drivers gphoto2 it has - are we sure it does not know your camera?

Would be a good start to read The gPhoto2 Manual - User's manual - Chapter 3. Frequently Asked Questions (FAQ).

Let's look for changes that added support for your camera in the changelog: http://www.gphoto.org/news/

Of course this is done manually, but for the text demonstration, I will use some shell commands

Are there any FinePix cameras supported officially at all?

$ wget -q -O -  http://www.gphoto.org/news/ | grep -i -o 'finepix.*' | tee finepix.txt

FinePix AV-150, T200

FinePix S4850, JX370, S4850

FinePix SL1000, S2980

FinePix: H20EXR, X20

FinePix S2950, S4300, X-S1, HS30EXR, XF1

FinePix F80EXR, X10

FinePix A220, Z700EXR

FinePix F60fd, F70 EXR, S1800, S5800

FinePix S1500, Z35, S2500HD

Finepix F200 EXR

FinePix S1000fd

FinePix A920, F100fd, S200HD

FinePix F20, F40, S9500

FinePix A330

FinePix S7000 (PictBridge mode)

Ok, a good start.

$ grep A900 finepix.txt

But ours is missing... maybe something similar?

$ grep A finepix.txt

FinePix AV-150, T200

FinePix A220, Z700EXR

FinePix A920, F100fd, S200HD

FinePix A330

Oh, A920 looks interesting... it's almost the same, actually! Same year, minor changes in lens etc..

Hey, wait!?! Could that work for our camera?

Maybe there is a feature request, or a bug, explaining why the camera is not known?

No feature request for the A900 found...

Let's look for something related, feature requests on FinePix, there are 16!

Let's see Support for Fuji Finepix A820:

• User with Finepix A820:
  
  I just bought a Fuji Finepix A820 and, although the camera is
  
  recognized as an ptp/ip camera, it isn't possible to access any photo.

  
  
  

  the (partial) lsusb output is:
  
  Bus 002 Device 008: ID 04cb:01c6 Fuji Photo Film Co., Ltd




• Developer of gphoto2:
  
  i have added the id.

  
  
  

  but this is likely a permission problem, it will probably work as root
  
  just fine.




• User:
  
  I tried running it as root and, as you said, it worked just fine. Nice!

  
  
  

  Nonetheless, running digikam as root isn't exactly desireable. Is
  there a way to avoid the root thing?




• Developer:
  
  usually your distributor provides a correct permission setup,
  please contact him.

  
  
  

  or read: http://gphoto.org/doc/manual/permissions-usb.html

That looks interesting, and similar; maybe it's even the solution we need to get it running?

They talk about fixing USB device permissions... it's from seven years ago, hard to tell how this still applies...
At least most pieces seem to be there... we need to read more...

But we do not need to develop a driver for the camera!

At this point, you need to plug the camera in, and play around with gphoto2 commands. Maybe try a test as root, to check for problems from missing permissions on device files...