ITF-14 is the GS1 implementation of an Interleaved 2 of 5 bar code to encode a Global Trade Item Number. ITF-14 symbols are generally used on packaging levels of a product. The ITF-14 will always encode 14 digits.
The thick black border around the symbol is called the Bearer Bar. The purpose of a Bearer Bar is to equalize the pressure exerted by the printing plate over the entire surface of the symbol, and to enhance reading reliability by helping to reduce the probability of misreads or short scans that may occur when a skewed scanning beam enters or exits the bar code symbol through its top or bottom edge. *

Labeljoy requires you to enter 13 or 14 digits to generate the barcode, depending on the settings in the Checksum combo box.
Enter the 13 digits in the text box if the Checksum options is set to Yes (the 14th digit will be automatically added), otherwise enter 14 digits.
The need of a checksum in position 14 may vary depending on the applications in use and the targeted barcode scanner settings.

ITF-14 symbol

The Frame combo box enables you to specify how the Bearer bars should be printed.

ITF-14 with horizontal only bearer bars ITF-14 with hidden bearer bars

Text concatenation:
When an ITF-14 barcode element is generated by concatenating fields or counters, the following rules apply:
- if the Checksum option is set to Yes, only the first 13 digits found will be considered, otherwise only the first 14 digits will be considered.
When a value not complying with the above rule is found, the barcode is not displayed.

The human readable text can also be shown above the symbol or hidden according to the setting specified in the Text combo box.

ITF-14 with text above the symbol ITF-14 with hidden text

* From wikipedia.