Most modern automatic image analyzers use an IBM or Macintosh computer. However some system still use a proprietary computer. I wouldn't consider a proprietary system. In fact a lot of manufacturers now just make the software and support a range of image boards. The problem with proprietary computers is that computer technology is progressing rapidly.
Service is another problem.
Computers service and parts are readily available for major computer brands. A proprietary make puts you at the mercy of the manufacturer. Most image analyzers can do image processing. Each analyser whether it is interactive, automatic or a filar will have a calibration routine. In industry it is common to use a N.I.S.T. traceable standard.