You can find names of methods that correspond to various Gimp operations via Gimp's PDB Explorer (menu Xtns/PDB Explorer). In this case it is gimp_image_scale. According docs avialable via PDB Explorer this function expects following parameters:

   In:
       IMAGE image
       INT32 new_width 
       INT32 new_height
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Perl module Gimp that provides bindings allows you to call this function as

    Gimp->gimp_image_scale($img, $new_width, $new_height);
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It also does some magick so you can call same operation under different names. All following calls do the same thing:

    Gimp->gimp_image_scale($img, $new_width, $new_height);
    Gimp->image_scale($img, $new_width, $new_height);
    $img->scale($new_width, $new_height);
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All you have to do is adding such call before saving jpeg file.

You can learn more from documenation in Gimp module and from Gimp-Perl web site.

--
Ilya Martynov (http://martynov.org/)