One-dimensional iDCT can be thought of as moving a digitized signal from the frequency domain into the time domain, but in the case of e.g. JPEG the two-dimensional DCT makes this analogy somewhat invalid.
Several hardware implementations exist for efficient iDCT, it is a common feature of MP3 players and some graphics cards, but iDCT can also be done in software, for example mpg123, a media player for UNIX, employ efficient assembler code for the iDCT step of MP3 decoding.