Hello Samuel,

Thank you for contacting Mearto with your appraisal inquiry. My sincere apologies for the delay with the appraisal.

The presented object appears to be a silver gelatine print with measurements of 40 x 30 cm. It is a portrait of Werner Kruger and is signed hand-signed in a fat felt tip pen by Richard SERRA (1939).

Sadly no additional information for an artist with this name fitting in style and motif is given by reference books and databases. 
Comparable objects were recently offered and sold on the international auction market. 
This piece is in good condition and there is no serious damage visible in the images provided.
A fair market estimation would be between 250 to 500 USD.
This estimate is based on actual recent past recorded auction sales of comparable items. Retail "asking prices" can be higher and may vary.

With kind regards, 

George