I.R.I.S. Readiris 14 for Windows User Guide - Manual (Page 78)

Section 7: Adjusting the Image Quality
84
To remove these little black spots, use the Despeckle slider. The
more you move it to the right, the larger the spots that will be
removed.
When you are done adjusting the image quality:

Click Apply to preview the results.

If the results are satisfactory, click OK. If not, change the
settings again.