Is Image::Size installed? Is it installed somewhere other than the directories in @INC?

perl -e 'print $_ . "\n" for @INC'
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That will show you what is in @INC. If it is installed elsewhere, use this in your script:

use lib qw(/path/to/it);
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Remember to use the path *up to* the Image directory. So, if it is installed in /home/you/perl/Image/Size.pm, use /home/you/perl
If it isn't installed, then:

perl -MCPAN -e 'install Image::Size'
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Cheers,
KM