mcomix doesn't prompt for a password, nor does it offer any option/control to assign passwords to archives (rar in this case) when unrar exectuable (as opposed to libunrar) is used.
I would expect either an "open with password" checkbox in the file-open dialog (if automatic fallback is not possible for any reason), and preferrably the option to assign a session-password (try that password with all rars that need password).
Hello,
MComix doesn't automatically detect the need for a password because it a) doesn't parse the output of unrar and b) the unrar command line is set up in such a way that no password is supplied by default. a) is due to unrar localization - parsing the text for x different languages isn't feasible. b) was done to prevent MComix from hanging up because it waits for unrar output forever, while unrar waits for password input.
Supplying a password in the open dialog might be an usable solution. Good idea. In the mean time, please consider using libunrar for password-protected archives (with the added benefit of faster extraction times).