Hello AskHistorians! All I know about this portrait of my grandfather is that the picture was taken in 1973 Francoist Spain, he most likely served within the armed forces or the Guardia civil. It is very hard to find any information about ranks back then and the closest thing I found was a rank table on wikipedia but the shoulder patch is very hard to identify, hence I came here seeking for help.
Hello there! As your question is related to looking for identification/information regarding military personnel, our Guide on Military Identification may be of use to you. It provides a number of different resources, including how to request service records from a number of national agencies around the world, as well as graphical aids to assist in deciphering rank, unit, and other forms of badges or insignia. While the users here may still be able to lend you more assistance, hopefully this will provide a good place to start!