First parameter of set_image_borders is not a source,

[haesleinhuepf]

it is actually a destination. This is a write-only functtion. I propose to rename it from "src" to "dst" here. Then, also this code two lines further down is less confusing:

const ParameterList params = { { "dst", src },...

[StRigaud]

this is related to kernels not the CLIc