I've been hoping someone else would suggest a solution for you because the only thing I can think of would be overly complicated.
Because you're on BP 5, it might be a little more difficult. But if I'm remembering Surface Automation functionality in BP 5 correctly, let me give some suggestions.
Wait stages used on an element for SA can have the condition of 'Is Uniform Color' or something like that. Depending on how important this business process is or how high the volume, you could come up with your own solution that maps out each file before reading it. I imagine this would involve dynamic regions that you increment/decrement vertically and horizontally to identify where the lines are and then you can read between the lines (no pun intended).
The problem I have with this is that BP 6 is way way way better for this. Not only does BP 6 have better Surface Automation, but it also has Intelligent Automation skills, which you can probably use to pass in your images and get an accurate conversion into structured data. Matter of fact, I think it would be worth it to stand up a second environment at your organization and use BP 6 in that for Processes that need the newer features.
Just something to consider. Much of what you do in BP 5 at this point that is not out of the box is likely reinventing a wheel that is already rolling in BP 6.
Dave
Dave Morris, 3Ci at Southern Company