I.R.I.S. Readiris 14 for Windows User Guide - Manual (Page 87)

Readiris TM 14 – User Guide
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Deleting small zones
Sometimes documents contain a lot of "noise" - little black spots
that occur when scanning low-quality documents or using bad
scanner settings. When that is the case, Readiris tends to mark them
as recognition zones, even though they do not contain any useful
content.
To exclude these zones from recognition:
 Click the option Delete small zones.
 This option erases all windows smaller than 0.5" and re-sorts
the remaining zones.
Ignoring zones on borders
When your scanner generates black borders around your
documents, Readiris tends to mark them as recognition zones, even
though they do not contain any useful content.
In such cases it is recommended to use the option Ignore zones on
borders. That way, the border zones will be excluded from the
recognition.