Unable to get aview to produce an image
EDIT: apparently if you invoke the program as asciiview instead of aview, it will automagically do the file conversion for you
asciiview somefile.png
Original answer:
The p?m refers to the libpnm family of "lowest common denominator" image files, including pbm and pgm. If you convert your image to one of those formats, for example using the convert tool from the imagemagick package
convert somefile.png somefile.pgm
(or using gimp if you prefer) it should work, e.g.
aview somefile.pgm