How to skip downloading files with certain extension using a config.json?

[Dobbelklick]

{
    "extractor": {
        "testsite": {
            "filename": "{id}_{date:%Y.%m.%d}_{content:CHgt/[:200]}.{extension}",
            "base-directory": "./testsite",
            "directory": ["{user}"] 
		}
	},
    "archive": "archive.sqlite3"
}

where would I put the config-analogue to something like --filter "extension != 'jpg'" to skip downloading jpg files without using site-specific options like "images":"no"? Everything I tried didn't work.

[kattjevfel]

"image-filter": "extension != 'jpg'",

[Dobbelklick]

Thank you!