The distinction between online and real picture galleries is to some extent blurred as some 'real' galleries make their artworks available via consortia and collective online virtual museums.
The Google Art Project presents high quality images from a number of major art galleries (76 hits for 'lute')
www.google.com/culturalinstitute/browse/lute?projectId=art-project
The Journal Music in Art, from Research Center for Music Iconography has lute-related material from time to time: rcmi.gc.cuny.edu/music-in-art/
Wien, Kunsthistorisches Museum (via Google Art project): www.google.com/culturalinstitute/collection/kunsthistorisches-museum-vienna-museum-of-fine-arts?projectId=art-project&hl=en
Paris, Louvre (10 hits for lute): www.louvre.fr/en/moteur-de-recherche-oeuvres?f_search_art=lute
Bayerische Staatsbibliothek, Munich, searchable image database: www.bsb-muenchen.de/en/catalogues-databases/digital-collections/image-search/
Wuerttemburgischer Landesbibliothek Stuttgart, Stuttgart Psalter (ff. 55, 69, 83, 97, 108, 112, 125, 161, 163): digital.wlb-stuttgart.de/sammlungen/sammlungsliste/werksansicht/?no_cache=1&tx_dlf%5Bid%5D=1343&tx_dlf%5Bpage%5D=1&tx_dlf%5Bdouble%5D=0&cHash=04474e0d6548da1963d57b38a1d2f29a
Amsterdam, Rijskmuseum (452 hits for 'luit'): www.rijksmuseum.nl/en/search?v=&s=&q=luit&ii=0&p=1
Madrid, the Prado: www.museodelprado.es/coleccion/
Prado sound of music in paintings project: www.museodelprado.es/investigacion/biblioteca/proyectos-de-investigacion/el-sonido-de-la-pintura-en-el-museo-del-prado/iconografia-musical-el-sonido-de-la-pintura-en-el-museo-del-prado
Cambridge, Fitzwilliam Museum, paintings drawings and prints: www.fitzmuseum.cam.ac.uk/dept/pdp/
London, British Museum Collection online (1116 hits for lute): www.britishmuseum.org/research/collection_online/search.aspx?searchText=lute
London National, Gallery (29 hits for lute): www.nationalgallery.org.uk/search?q=lute&x=22&y=10
National Trust Collections: www.nationaltrustcollections.org.uk/results?SearchTerms=Lute Some of the most important lute paintings in National Trust properties were discussed in a series of front cover illustrations of Lute News, issues 90-97, www.lutesociety.org/pages/lute-news-back-issues
The Public Catalogue Foundation has digitised all the circa 210,000 oil paintings in public ownership in the United Kingdom, and made the paintings viewable by the public through a series of affordable catalogues and, in partnership with the BBC, the "Your Paintings" website www.bbc.co.uk/arts/yourpaintings/. Works by some 40,000 painters are included. www.thepcf.org.uk/
New York, Metropolitan Museum of Art (836 hits for lute): www.metmuseum.org/collection/the-collection-online/search?ft=lute