When generating bar codes as image stream, the bars (or spaces) should always be aligned on the pixel grid of the generated bitmap.
Note: Without any scaling images in a browser are always displayed in 96 dpi. A thin bar having 1 pixel is normally 1/96 inch wide.
Principally, you shouldn't have any problems printing 96 dpi image on a laser printer with 600-1200 dpi. There are some printing tolerance which may occur while converting 96 dpi to 600/1200 dpi but they are minimal.
In ASP the CountModules, XRows, XCols functions can be used for adjustments. Look at the ASP and PHP samples delivered within the setup. For ASP.NET refer to the sample code below.
It might eventually be more complex to adjust the barcode to a specific size or to adjust the printing resolution to 300 dpi or lower. In this case, you should adjust the barcode module width to the dot-width of the printer.
See section A.4 in the Barcode Reference for more information. We recommend reading the whole Appendix A starting with page 83.