The $dbh is already a blessed reference (=object), so just write: my $result=SelectProfile($id, $dbh);

An interesting idea might be:

my $result = $dbh->SelectProfile($id);
....
package DBI; # or whatever package shell be extended

sub SelectProfile {
  my ($self, $id) = @_; # $self is $dbh
  my $selectquery = "SELECT *
                     FROM people
                     WHERE id = '$id'";

        my $sth= $self->prepare($selectquery)
          or die "Error in prepare: $DBI::errstr\n";
        $sth->execute()
          or die "Error in execute: $DBI::errstr\n";

        my $rowdata=$sth->fetchrow_hashref;
        $self->disconnect; # imho better done in main-program...      
+     
         return $rowdata;
}##END SelectProfile
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I suggest to evaluate returncodes if there's the slightest possibility that an error happenes, so nearly all the time.

Best regards,
perl -e "print a|r,p|d=>b|p=>chr 3**2 .7=>t and t"