Many of the functions and effects in IrfanView can be
applied to just a portion of an image, rather than the
whole. To use them so, you need to outline the area on
which the work will be performed.
The actions that can be taken on an outlined area are
From the Edit menu:
Add Text, Cut, Crop, Copy
From the Image menu:
and the Effects:
3D Button, Blur, Emboss, Oil Paint, Edge Detection,
Median Filter, Explosion, Pixelize, Fine Rotation,
Filter Factory filters
All of the above actions (excepting Copy) can be
reversed using the Edit menu Undo option.
You can perform different actions on different areas
of the image, even overlap them for extra special