Marginal differences shouldn't fail the test (there should be an option for this - sometimes a marginal failure is important)

Caraya supports a margin of error when comparing floating point numbers (as 10.0 != 10.0 exactly)

I found a similar issue when generating png images and trying to compare them. The two attached images were generated by exactly the same configuration script and look identical, but not when you put them through a compare tool - however for my purposes they're close enough (its the ends of the error bars that are 1 or 2 pixels different).

Its not urgent as the work around is to compare the configuration script, which is generated from a list of parameters - and that's what I'm really trying test

Start by tracing the image-comparison path and the existing floating-point margin-of-error behavior; the issue does not name specific files or tests. Define how an optional image tolerance should work while preserving strict comparisons by default, then add coverage showing that small pixel differences can pass and meaningful differences still fail.