Actually, as a final "fix" to the whole thing -- do you actually need the latest image file to be kept on the file system, or are you just keeping it there to compare against the next fetch? If you do not need the image on the file system, you can bypass that altogether and just use the database:

#!perl -w

use strict;
use DBI;
use LWP::Simple;

my $img_url = "http://weather.unisys.com/satellite/sat_ir_west.gif";

my $dbh = DBI->connect(
    'dbi:mysql:weather_images', 'user', 'secret', {
        RaiseError => 1, AutoCommit => 1
    }
);

my ($min, $hour, $day, $mon, $year) = (localtime())[1..5];
$year += 1900;

my $img_name = "$mon-$day-$year-$hour:$min";
my $img_data = get($img_url);

die("failed to fetch image from internet!\n")
    unless ( defined($img_data) );

# fetch the last row we added to the table
my $latest_entry = $dbh->selectrow_arrayref(
    'SELECT image_file FROM gw_ir ORDER BY image_id DESC LIMIT 1'
);

# either no data in database or the file contents
# have changed since the last update
if (not defined($latest_entry) or $latest_entry->[0] ne $img_data) {
    $dbh->do(
        'INSERT INTO gw_ir (image_name, image_file) VALUES(?,?)',
        undef, $img_name, $img_data
    );

    warn("File was not current; updates made.\n");
}

else {
    warn("File was current, no updates made.\n");
}

$dbh->disconnect();
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And even if you do need the file system file, it might even be better to use the database anyway and then output the file:

#!perl -w

use strict;
use DBI;
use LWP::Simple;

my $img_url = "http://weather.unisys.com/satellite/sat_ir_west.gif";
my $local_img = "/usr/home/mhearse/weather_images/latest.gif";

my $dbh = DBI->connect(
    'dbi:mysql:weather_images', 'user', 'secret', {
        RaiseError => 1, AutoCommit => 1
    }
);

my ($min, $hour, $day, $mon, $year) = (localtime())[1..5];
$year += 1900;

my $img_name = "$mon-$day-$year-$hour:$min";
my $img_data = get($img_url);

die("failed to fetch image from internet!\n")
    unless ( defined($img_data) );

# fetch the last row we added to the table
my $latest_entry = $dbh->selectrow_arrayref(
    'SELECT image_file FROM gw_ir ORDER BY image_id DESC LIMIT 1'
);

# either no data in database or the file contents
# have changed since the last update
if (not defined($latest_entry) or $latest_entry->[0] ne $img_data) {
    open( my $fh, '>', $local_img ) or die("could not open file: $!");
    binmode($fh);
    print $fh $img_data;

    $dbh->do(
        'INSERT INTO gw_ir (image_name, image_file) VALUES(?,?)',
        undef, $img_name, $img_data
    );

    warn("File was not current; updates made.\n");
}

else {
    warn("File was current, no updates made.\n");
}

$dbh->disconnect();
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