I know that if it were Oracle database, I could simply execute a query like this:

select description, image, org, level from category
connect by parent = prior id
where id = '$id'
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This would return hierarchy like structure (parent rows followed by child). level is a special 'hidden' column that is appended to the results of hierarchical queries. This column simply holds a number representing 'level' of the category. So, top most parent will have level of 0, and so on.

Unfortunately, as per this document Things That Must be Done in the Near Future this feature has not yet been implemented in MySQL. However, they promise us the work is being done in this regard ;)

In the mean time, I'd like to suggest a few enhancements to your code. Things that should speed your process are caching your query and also using value bindings instead of generating ever changing query string (since $id is changing...)

(@fer) = find_all_categories();
sub find_all_categories {
 $id = shift;
 if($id) {
  $sthm = $dbh->prepare_cached("SELECT * FROM category WHERE id=?");
  $sthm->execute($id) or die $dbh->errstr;
 } else {
  $sthm = $dbh->prepare("SELECT * FROM category");
  $sthm->execute or die $dbh->errstr;
 }
 while (@hi = $sthm->fetchrow_array) {

 if($hi[2] eq "0") {
   push(@env, @hi[0])
 } else {
   $a = find_all_categories($slog[0]);
   $i += $hi[3];
   $i + $a;
 }

 }
 push(@env,$i);
 return(@env);
}
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# Under Construction
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