Oh VICAR is not so strange. There was this "weird" habit back then that the file formats (IMG astronomical format does this too) would start with an ASCII-based

Oh VICAR is not so strange. There was this "weird" habit back then that the file formats (IMG astronomical format does this too) would start with an ASCII-based fixed length header (or the header is variable size, but has a line of text at the start that states the size). Always a multiple of 512 or 1024 bytes too. And then in the header you can literally read (with your human eyes) the format used, how many bits per pixel, the lines width and how many lines and so own. You can literally write a parser from reading a couple of headers. Of course, it's much better to be provided with software that can handle all the nuisances of the format without having to test it when something fails on you.