All I can discover about this photo is Luis Echeveria, the Mexican president from 1970-76 is pictured front left, and the photo was taken at Casa De Carranza (that is Carranza in the painting). However, I don't know exactly when the photo was taken, or who else is in the photo (I can only assume people close to the deceased, whoever that is, or possibly cabinet members, politicians, etc.). If you can assist in discovering more information, even the smallest details, would help a ton.

Photo to follow in the comments.