Question: irfanview how to compress image?
Answer: Open Irfanview, and click on File, in the Toolbar, and select Open.
In the box that opens, navigate to the image you want to reduce the file size of, and select it (single Left click). ... 
The image will open up in the Irfanview window. ... 
When the Save Picture As... ... 
This will open the JPEG/GIF save options dialog box.