There are several possible syntaxes, depending on how your brain likes to work ;-)
What you need to bear in mind when trying to understand this is that all processing operations, e.g. -crop or -resize apply to all loaded images. So, you either need to load images that need processing and process them before loading images you don't want affected, or you need to restrict processing to certain images only... using parenthesised "aside" operations.
You can proceed like this:
- load transparent foreground image first and process it before loading the background image, then
- load background image, then
- exchange the order and composite
That looks like this:
magick FOREGROUND.PNG -resize ... -crop ... \
BACKGROUND.PNG \
+swap -composite RESULT.JPG
Alternatively, you could:
- load the background image, then
- load the foreground image and process it "aside" within parentheses so that the background image is not affected
- composite
That looks like this:
magick BACKGROUND.PNG \
\( FOREGROUND.PNG -resize ... -crop ... \) \
-composite RESULT.JPG
If you need to independently process both background and foreground images prior to compositing, use:
magick \
\( BACKGROUND.PNG -resize ... -crop ... \) \
\( FOREGROUND.PNG -resize ... -crop ... \) \
-composite RESULT.JPG
Note that if you use Windows:
- the backslashes at line-ends become carets (
^) and may not have trailing spaces after them,
- the backslashes preceding opening and closing parentheses must be omitted,
- most single quotes probably need replacing with double quotes - probably not applicable to this specific question.
Note that your command is probably unnecessarily complicated, I would recommend omitting quite a lot of it and seeing how you get on. For example, all the define png:XXX=YYY settings are irrelevant if you aren't creating a PNG as output.
You can carry forward the JPEG-related parameters (quality, interlace, upsampling) and put them in anywhere you like, probably at the start like this, but put the colorspace and strip at the end to ensure both input files are stripped:
magick -quality 82 -define jpeg:fancy-upsampling=off \
BACKGROUND.PNG ... \
FOREGROUND.PNG ... \
-composite -colorspace sRGB -strip RESULT.JPG
