my %image_hash = ( );

while (<IMAGEHASH>) {
    # Limited scope of $search/$replace
    # You could just use split to split on whitespace:
    my ($search, $replace) = split;

    # Or if you want to split on the first single space character, and force only 2 items:
    # my ($search, $replace) = split ' ', $_, 2;

    # or you could use a regex:
    # my ($search, $replace) = m/([^ ]*) (.*)/);

    # Suppress uninitialized warnings.
    # check for non-zero length, 
    # although eq '' checks should be fine, too.
    {   no warnings 'uninitialized';
        if ( length $search and  length $replace ){
            warn "Found uplicate entry for: $search\n"
                if exists $image_hash{$searc};

            $image_hash{$search} = $replace;
        }
    }
}