Perhaps the names are not exactly the same? You do have leading zeros?
So the problem is the .jpg on the end. When you tell FM that the filename is matched with a field, it includes the .jpg.
The way I figured this out, and got around the problem was created a calculation field that added .jpg to the end of my barcodes (in my db). Since you cannot import by matching using a calculation field, I switched the new field to 'text' from 'calculation', which retained the calculation results. I then imported the pictures matching the filename to the barcode.jpg field instead. This worked and I now have the pictures in the correct container field.