You can find fonts that you can install for printing most barcodes. You simply enter your data for the code and a copy of that same field formatted with the font will display barcode. But many such barcodes include extra characters, such as a "check digit" that have to be included to produce a valid code. But a calculation field can be set up that takes the data you've entered and combines it with the needed extra characters.
In addition, UPC codes have to be "registered" with the appropriate organization to confirm that your codes are both valid and unique.
I have had a heck of a time trying to figure out bar codes for FM - here is how I generate barcodes. On my computer, I have installed bar code fonts (freely available on the web). If I have a layout in Filemaker where I want to display the barcode, I simply have that field formatted for the bar code font. This works well and because it is still technically text it is very light on the database (vs an image).
The problem lies in printing the bar codes from a remote device running FileMaker Go or using FileMaker Web Direct:
If your solution prints bar codes from FileMaker Pro on your desktop, you will have no issues.
However, if you want to print from a remote source as in FileMaker Go or Web Direct you will certainly have limitations and you will need to generate a bar code image - (I used Geist Interactive bar code generator - it generates a bar code image from a set of scripts that they sell you) works really well.
The limitations I speak of above:
FM Go - the iOS version does not support bar code fonts (as of this writing) so your text will show as raw text and not bar code font text - you can print it from FM Go using AirPrint or Printopia, but it won't print a bar code unless it's an image.
Web Direct - Web direct does show the fonts nicely if you have them installed on the remote computer, but Web direct doesn't support the Print script step so you can see it but not print it.
I hope this helps. BTW, you mentioned Google as a source of your bar codes - I am not familiar, can you send a link?