Mona Lisa
Leonardo da Vinci is thought by some to have begun painting the "Mona Lisa" in 1503 or 1504 in Florence, Italy. Although the Louvre states that it was "doubtless painted between 1503 and 1506", the art historian Martin Kemp says there are some difficulties in confirming the actual dates with certainty. In addition, many Leonardo experts, such as Carlo Pedretti and Alessandro Vezzosi, are of the opinion that the painting is characteristic of Leonardo's style in the final years of his life, post-1513. Other academics argue that, given the historical documentation, Leonardo would have painted the work from 1513. According to Leonardo's contemporary, Giorgio Vasari, "after he had lingered over it four years, [he] left it unfinished". Leonardo, later in his life, is said to have regretted "never having completed a single work".
Circa 1504, Raphael executed a pen and ink sketch, today in the Louvre museum, in which the subject is flanked by large columns. Experts universally agree it is based on Leonardo's portrait of "Mona Lisa". Other later copies of the "Mona Lisa", such as those in the National Museum of Art, Architecture and Design in Oslo and The Walters Art Museum in Baltimore, also display large flanking columns. As a result, it was originally thought that the "Mona Lisa" in the Louvre had side columns and had been cut. However, as early as 1993, Zöllner observed that the painting surface had never been trimmed. This was confirmed through a series of tests conducted in 2004. In view of this, Vincent Delieuvin, curator of 16th-century Italian painting at the Louvre museum states that the sketch and these other copies must have been inspired by another version, while Frank Zöllner states that the sketch brings up the possibility that Leonardo executed another work on the subject of Mona Lisa.
Portrait of Dorothea Berck
Portrait of Dorothea Berck is a 1644 painting by Frans Hals that is in the collection of the Baltimore Museum of Art. It depicts Dorothea Berck at age 51, the wife of the prosperous Haarlem merchant Joseph Coymans, whose portrait Hals also painted. Both paintings were executed on the occasion of their daughter Isabella's wedding, whose marriage pendants Hals also painted.
The painting, like many of Hals's portraits, is inscribed and signed, but there is no mention of the identity of the sitter, and it was only identified as Berck in 1908. 
The portrait is noted for its classical similarity to the Mona Lisa. Like the Mona Lisa, she sits upright in a dark chair and rests her hands on either a dark desk or perhaps a large dress that surrounds her. Her ungloved hand may be clasping a book or part of her sleeve. The loose brushwork is typical of Hals and shows a fleeting gesture with the casual way her finger is hooked over her wrist. Portraits of subjects with one glove on and one glove off are common in Dutch 17th-century marriage pendant portraits. Gloves symbolize the wedding vows where the husband and wife each hold one of a pair of gloves. In this case, her husband Joseph Coymans is wearing the "other glove" in his pendant portrait. In Hals' marriage pendant portraits, the husband is always situated on the left and the woman on the right, and the light always comes from the left, shining fully on the woman.