Janssens contributed to the genre of the 'gallery paintings'. The 'gallery paintings' genre is native to Antwerp where Frans Francken the Younger and Jan Brueghel the Elder were the first artists to create paintings of art and curiosity collections in the 1620s. Gallery paintings depict large rooms in which many paintings and other precious items are displayed in elegant surroundings. The earliest works in this genre depicted art objects together with other items such as scientific instruments or peculiar natural specimens. The genre became immediately quite popular and was followed by other artists such as Jan Brueghel the Younger, Cornelis de Baellieur, Hans Jordaens, David Teniers the Younger, Gillis van Tilborch and Hieronymus Janssens himself. A good example is the "Picture Gallery with Fashionable Visitors" (National Trust, Uppark House and Garden, West Sussex) dated to the 1660s. The gallery depicted is an imaginary gallery with three allegorical figures who are admiring a canvas of the 'Last Judgement'. On a table by a window are placed pieces of sculpture, a globe, and other objects. The contrast between the precious objects on the table and the 'Last Judgement' in the foreground illustrates the idea of vanitas: the ultimate vanity of earthly pleasures. His work was of influence on later Flemish genre painters such as Jan Josef Horemans the Younger, whose work "Presenting the newborn" (current whereabouts unknown) borrowed extensively from Janssens' "" (Palais des Beaux-Arts de Lille).