I did ... but not in the way it is specified in the manual of Imager::Files. Thanks for hinting it is possible as I was convinced it wasn't and did not perservere with the manuals ... (maybe they should put this important info under the heading read() or in the Description section of mod:://Imager). The following works for me:

use strict;
use warnings;

use Imager;
use Imager::Filter::Autocrop;

my $imgdata = undef;
open(IN, '<', 'example.jpg');
binmode(IN);
{ local $/ = undef; $imgdata = <IN> }
close(IN);

my $img = Imager->new();
# possible params are 'file', 'data' and 'fd'
$img->read(data=>\$imgdata) or die "read: ".$img->errstr();

$img->filter(type=>'autocrop', fuzz=>20) or die "autocrop: ".$img->err
+str();
$img->write(file=>'out.jpg') or die "writing: ".$img->errstr();
[download]

Edit: actually it is not documented in Imager::Files that data is a recognised input param name for read(). It is only mentioned in the write(). Anyway, all well now.