The company was a major publisher of heliotype, black-and-white postcards. It also produced gravure and tinted cards. Heliotype printing involved exposing a gelatin film under a negative, hardening it with chrome alum, and printing directly from it.
Some Rotophot series also appear with ELD branding, presumably because they were more easy to sell in France - though this happened with German publishers too. For example cards of set RPH 2091 appeared as ELD 8000 and PFB Series 16.