How do I say that? L'autre image est plus drôle que ce ca? I don't understand how to build the last part, please help me.
The other picture is funnier (than this one)
would be translated as:
L'autre image est plus amusante (que celle-ci).
"Celui-ci, celle-ci, ceux-ci, celles-ci" are "pronoms démonstratifs" that need to agree in gender and number with the thing they refer to. Here, "image" being feminine, in the singular, "celle-ci" is what you need, and for the plural "celles-ci".