Dear maintainer,

TL;DR: I suggest changing the Depends on libopencv-dev to a
Recommends.

CImg is, according to the projects description, a "small" library. Yet
the Debian package cimg-dev does depend on libopencv-dev, which pulls in
another 500MB of packages (unpacked size).

CImg can use OpenCV if you define cimg_use_opencv, but it can be used
without it. I found 3 packages build-depending on cimg-dev (beads,
jkqtplotter, tiv), and none of them seems to utilize OpenCV. So removing
or demoting the libopencv-dev dependency to recommends/suggests should
not cause an issue.

I can successfully compile small examples from the CImg tutorial without
libopencv-dev installed.

Is there a reason did not find for a dependeny on libopencv-dev?
Otherwise I would suggest to demote the dependeny to a recommends, like
the other libraries useable by CImg.

The same goes for libimath-dev, but thas is only a small package
compared to OpenCV with dependencies.

Thanks,
    Ingo