The closest you can do, I think, is this:
codegen ProcessImage -args {coder.typeof(uint(0), [Inf Inf]) } -config:lib
This would generate ProcessImage.c that takes an unbounded 2-d array of uint8 as input. Coder would also generate main.c (in the examples folder) that shows how to allocate and initialize the data structure that ProcessImage.c takes as input.
From there, you can write a simple wrapper that takes a pointer and two sizes and produces the emxArray_uint8_T data structure that coder-generated code takes as input. You can set the "canFreeData" to false and then you don't need to copy the actual values, can just copy your pointer into the emx structure.
