Feature based optional dependencies

[bencevans]

The core functionality should be available with pip install camtrapml, e.g. image processing and filtering.

Features that require a more heavy set of dependencies, such as Exif extraction, detection and classification tooling, should require installation as options e.g.

pip install camtrapml[md4]
pip install camtrapml[md5]
pip install camtrapml[exif]

Everything with something along the lines of

pip install camtrapml[md4,md5,exif]