The current setup is really weird and definitely wrong for many cases
because it inverts the colors of the image, which is never a good idea
for GUIs. So, try to OCR three different times: once on the source image,
once with processing, and once with processing but no negation.
This should hopefully make things work at least somewhat better for GUIs.
Specifies the "last try" parameter in all methods called by `retry`.
Doing this clarifies its presence, and makes it easier to use it in the
future if needed.
I don't know why it doesn't want to do TIFF now, but there's also
absolutely no reason for it to be TIFF anyway, so let's just use
an image format that is actually sane.
