Here's a bit more on transparent sections. Powerpoint has a feature to remove the background of an image that is oftentimes simpler and faster than Irfanview. Basically you insert an image onto a slide, then select the image and use Picture Tools>Format>Recolor>Set Transparent Color. A pencil icon will appear that you use to select the background to be removed. Then right click on the image and select Save As Picture. The saved picture can then be inserted into your Word document.

With regard to checking the transparency of an image, an easy thing to do is to copy the image into Excel. The gridlines will be visible in the transparent sections.