The custom is rooted in pre-Christian rites of evoking the nature after winter solstice (after ‘New Sun’ when the days start growing longer), and is still practiced in Poland throughout January and beginning of February each year - during the whole carnival season.
In these rites groups of people dressed in symbolic costumes with musicians are wandering from house to house in a joyful parade, creating noise (e.g. ringing bells and singing loudly) and pulling harmless pranks, all in order to put the community in a festive mood. The popular costumes included on the pictures are for example ‘bears’ (which symbolize waking up from the winter hibernation), ‘death’ (beginning of something new), ‘devils’ (winter darkness and evil forces in nature) and the most important ‘dziady’ (symbolic ‘ancestors’ - souls of the deceased wandering on the Earth).
It’s observed under many different local names in Poland, and the term of the general custom - kolędowanie - comes from the word kolęda, which is associated with Christmas carols nowadays but originally meant simply a joyful New Year’s song in old-Polish.
This annual festival is connected to the general custom of kolędowanie, Slavic new year’s rites of old pagan origins in which people celebrated the days growing longer after the winter solstice [read more here].