Whether the company's behavior is legal: generally speaking, the picture provider should provide copyright fees to the author and use the right to use it to monopolize the relevant copyright. It is completely legal and reasonable for them to let you know through the circular letter. Don't be nervous, the other party needs to show that the copyright of the picture really belongs to them.
Chance of winning the case: once it is proved that the copyright or communication right has been infringed, the other party is likely to win the case, and in some cases, the legal fees and attorney fees may also be borne by the losing party.
Lawyers told us that protecting intellectual property rights and being aware of copyright is not only protecting others, but also protecting us, which deserves attention. In addition, don't worry about being sued, please delete the relevant articles in time, and don't reply to the notification letter to avoid admitting the facts.