Denner was a master of Feinmalerei, or fine painting. He concentrated almost exclusively on bust-length portraits of elderly subjects. He rendered every wrinkle and skin fold with a clinical accuracy that stood apart from the broader brushwork of the French and Italian styles. This approach was not intended to be cruel. Instead, he treated the signs of age with a quiet respect. His subjects, such as the sitter in Portret van een man, appear in a soft light that balances realism with a sense of dignity.

Modern collectors value Denner for his uncompromising honesty and technical skill. His work lacks the artificiality often found in eighteenth-century court portraiture. These prints offer a direct connection to the past through their focus on human reality. The neutral backgrounds and tight compositions make them suitable for contemporary interiors. They function as studies of character and time rather than mere status symbols.