From the Output Filename section of the command-line processing web page:
Standard Out
Unix permits the output of one command to be piped to another. ImageMagick permits piping one command to another with a filename of -.
In this example we pipe the output of convert to the display program:
magick logo: gif:- | display gif:-
Your command-line could then start with:
convert -thumbnail 1024 test.JPG -
... or optionally converted to other formats with the proper prefix:
convert -thumbnail 1024 test.JPG png:-
... at which point you could then pipe that output to your blob-store-reader:
convert -thumbnail 1024 test.JPG - | blob-store-reader
