public function integer of_get_image_size (readonly blob abb_image_data, 
                  ref unsignedinteger ai_width, ref unsignedinteger ai_height, 
                  ref string as_measure);
Long ll_i, ll_start =  0 
Byte lc_dp

// Find JFIF header start
For ll_i =  1  To Len(abb_image_data)
   If String(BlobMid(abb_image_data, ll_i,  4 )) = "JFIF" Then
      ll_start = ll_i
      Exit
   End If
Next
If ll_start =  0  Then Return - 1 

// Read measures
lc_dp = byte(BlobMid(abb_image_data, ll_start +  6 ,  1 ))
Choose Case lc_dp
   Case  1 
      as_measure = "DPI"
   Case  2 
      as_measure = "DPC"
   Case Else
      Return - 1 
End Choose

// Read resolution
ai_width = Integer(BlobMid(abb_image_data, ll_start +  7 ,  2 ))
ai_height = Integer(BlobMid(abb_image_data, ll_start +  9 ,  2 ))
// Reverse byte order
ai_width = Integer(ai_width *  256 ) + Integer(ai_width /  256 )
ai_height = Integer(ai_height *  256 ) + Integer(ai_height /  256 )

Return  1 
end function

blob{ 4 } lbb_tmp
long ll_dc
BlobEdit(lbb_tmp,  1 , Long( 0 ))
BlobEdit(lbb_tmp,  1 , BlobMid(abb_image_data, ll_start +  6 ,  1 ) )
ll_dc = Long(lbb_tmp)

 8 -bit unsigned integers, from  0  to + 255 .
Using literals  To assign a literal value, use any whole positive number in the range  0  to  255 .
The leading plus sign is not required ( 18  and + 18  are the same).
For example: 
 1   123   200  + 55  + 200