# Establishing the Region of Interest

After acquiring an image with examples of characters that you want to identify in your complete vision application, you must define a region of interest to surround the string:

Ideally, the region you specify should have the following qualities:

- It should surround only the characters in the string and no other features.

  See the section Guard Against Border Fragments if it is possible that miscellaneous features can occasionally penetrate the region of interest.

- It must surround only one line of characters.

  Multiple lines of characters require multiple OCRMax tools.

- It must occupy as large an area of the image as possible considering the optics in your production environment.

- Ideally there should be the width of half a character between any character in the string and the border of the region.

By default, the tool uses an affine rectangle for the region of interest. Although you can change this default and specify the OCRMax tool use the entire image, this can severely impact the performance of the tool. Cognex strongly recommends you use an affine rectangle whenever possible.

See the following sections for more information: