I do know a bit about image manipulation. I am not an expert, by any means, and I have never tried falsifying a document, but I figure I could reproduce the purported BC. It would take time, though. In a few minutes I was able to produce a couple of minor changes that suggest I could modify the Australian BC:
Notice that I changed the book and page number, and began tinkering with constructing the "Coast Province of Kenya" phrase. That stopped me because I found that there was no upper case "K" in the document to copy and massage into place. Any attempt to create that "K" would be tedious and, unless expertly done, would stick out like Obama's ears.
It would be much easier to find a similar font and write the text as desired, then drop it in a layer over the template. Simply by resizing and playing with the DPI settings, it would be easy to reproduce the JPEG compression artifacts seen around the other text.
To create the bogus BC I'd make a template of the underlying government form with a similar font using Microsoft Word or a desktop publishing software application. I'd convert that to an image and drop in the text copied and assembled from the Australian BC. Finally, I'd print it, fold it, put it in my back pocket for a while, then unfold it and repeat as necessary. When I was satisfied with the result, I'd photograph it, not scan it. I'd make sure I shot it with a bit of perspective to mask any imperfections. There’s a reason we don’t see a simple scan like the Australian BC.
Why bother assembling the typewritten text like a ransom note from an old movie rather than just using a font substitution? I would do it because a substitute font might be easily recognized. One reason I think someone did assemble the text from the available typewritten characters is because the uppercase components of the deputy registrar's names are so similar: "YOUNG" and "ODUYA". The "D" is easily copied from "Douglas" and the "A" bears a distinct slant to the left that jars with the "ODUY". I don't see a similar "A" elsewhere in the Australian document, so it may just be sloppiness in skewing the character.
I cannot explain why someone who would use an Australian BC as a template would leave any significant elements unchanged. Perhaps the culprit used OCR (optical character recognition) to collect the text, then forgot to change it. I’ve done that sort of thing.
That’s as far as my eyes and thinking take me for now. Fwiw.