"This ETS specifies the data syntax to be used by Videotex services for conveying photographic data. In general@ it applies to the interchange of photographic data via storage or transmission media. The ETS is applicable to Videotex terminals connected to various types of telecommunication networks including; a Public Switched Telephone Network (PSTN)@ a Public Switched Packet Data Network (PSPDN) or an Integrated Services Digital Network (ISDN). For the ISDN case@ these terminals will typically support ""ISDN Syntax-based Videotex"" (see ETS 300 079 [3]). The syntax allows for some private extensions beyond the transmission of still pictures. For example@ a provision has been made for the transmission of a ""difference"" image to allow a slow scan television type of application."