Photo credit: Salford Museum & Art Gallery
Could this by Francesco Furini (1603–1646)? Compare this with his 'Sigismondo with the Heart of Guiscardo' in the Birmingham Museums Trust collection: https://artuk.org/discover/artworks/sigismunda-with-the-heart-of-guiscardo-33217/
Cleaning this picture should clarify its subject as well as to which Florentine seventeenth-century artist painted it, and as to whether it is an original, a studio version or a copy.
The collection comments: This painting came into the museum collection in 1868 and it is thought that the title 'The Duet (Scene from an Opera)' is one given to it in the nineteenth century. The original title is more likely to have been a scriptural one.
The painting is unsigned and is recorded in the documentation as anonymous, Italian, seventeenth-century. Sewter thought it might be by Guercino but it has been restored so much that attribution is difficult.
I think this might be Simone Pignoni.
Might the subject matter conceivably be from 2 Samuel 11 et seq. ? - Bathsheba, wife of Uriah the Hittite is distraught over her husband being killed in battle at the siege of Rabbah. But she is pregnant by the King who has seduced her in Uriah's absence. David had secretly arranged for Uriah's death by putting him in the hottest part of the battle. David is identified with his symbol of a viol.
The suggestion of Furini or one of the Furiniani like Pignoni seems eminently sensible to me, but unlikely to be provable in the current state of the painting and/or photograph.
This painting might depict the story of Adonis resisting Venus, as painted by Guercino (aka Il Guercino, aka Giovanni Franceso Barbieri) (1591 - 1666). It is a theme that he explored in another work, since destroyed, that was in the Dresden Museum collection. A Google search of images for Guercino will return many paintings of a similar style and classical theme. This work is also likely to be the 'Allegorical Painting' that is listed as part of the donation of Thomas Agnew (the great art collector and dealer) which he gave to Salford Museum in October 1868. The Birmingham Gazette of Saturday 21st November 1868 gives a full list of all the pictures that were given by him, which might also help with the identification of other unattributed or unidentified works in the Museum's collection. As no Guercino is listed on the Salford Museum's set of images on the ArtUk website, and no other work donated by Thomas Agnew is by an unknown artist for this period, it is worth considering the Guercino attribution.
Is the subject not Orpheus and Eurydice? Orpheus is often depicted with a violin instead of a lyre:
Tim, most certainly you are correct, as I now see from various other depictions of the same subject. However, it still might be the allorigical painting described as part of Thomas Agnew's 1868 donation to Salford Museum. Looking at the list of this particular gift, there seems to be no other contender.
A beautiful painting by Simone Pignoni.
Tim has I think correctly identified the subject as 'Orpheus and Eurydice'. The attribution remains uncertain but I think it can be at least 'attributed' to Simone Pignoni.