Currently Being ModeratedNov 22, 2013 1:53 PM (in response to BobKorver)
Voila will do screen grabs masked to circles (or ellipses). Any graphics program should allow you to layer a vector-mask over a background image. You might be able to do circles with Preview.
Note that in all cases the image file remains rectilinear. The pixels between the image border and the circle/n-gon mask are rendered as transparent, so you see a circular (or n-gonal) image, but the file contains information on the entire enclosing rectangle.
Message was edited by: Kirby Krieger — minor changes.
Currently Being ModeratedNov 22, 2013 2:04 PM (in response to BobKorver)
Preview - comes free with every Mac - can crop to ellipses or free-form shapes.
Open your photo in Preview and enable the "Edit Toolbar" from the "View" menu. Click the dashed rectangle to reveal the selection menu and select the ellipse.
Draw the crop ellipse you want and copy it to theclipboard. Then select "File > New image from Clipboard and you will get a cropped rectangular image with the ellipse on a transparent background.
To crop your other shapes, use the "Lasso" selection.
Currently Being ModeratedNov 22, 2013 4:56 PM (in response to léonie)
The Edit Toolbar in my Preview (Version 6.0.1 (765.6) on 10.8.5) has a "Elliptical Selection" tool. Just select and hit the crop icon on the Edit Toolbar. No need to make a new file. If the file format does not allow transparency, Preview offers to save it as PNG (which does).
(PS: About those four Adobe updates ... .)
Currently Being ModeratedNov 22, 2013 10:32 PM (in response to Kirby Krieger)
for a png or any file format, that supports transparency, your method is perfect. But if you start with a jpeg, I find it easier to create a new image from the copied selection in the clipboard, otherwise preview will only offer to replace the existing file by a png file, not to create a new file.