How to make white portions of the picture pasted to excel transparent

I regularly take screen shots of graphs generated by another program and paste them to excel to comment on. Majority of the area in these pasted pictures is white. Is there a way to make just the white transparent so that I can write comments in the cells that are behind the picture and have them be visible? Tried using the textbox but it takes too long to set up every time.

Thanks

In what format are the images saved? If you save them in a format that supports transparency, that may work. If you are copying and pasting, or just screenshotting and pasting, then they will come over as bitmaps, which do not support transparency. There is no way I know of to make their backgrounds transparent in Excel itself.

Hi Ali, I'm just screen-shoting and pasting. I though it might be complicated so posted to the forum, but with a bit of playing around figured it out:
Select image > Format > Color > Set Transparent Color > click on white portion.

Ooh, good to know!