Using Preview Mask in Instant Alpha

I have an IMAC with OS X 10.5.8 2GHz Intel and have been using Preview to extract some edges on photos that I import into a PPT presentation.

I was successful for a long time...and now for some reason, I forgot the procedure and no longer see a menu pop up that offers INSTANT ALPHA or EXTRACT SHAPE. I have tried putting the images in TIFF, Jpg, png, and pdf and still can't do it. Can someone tell me the procedure for this? I looked it up in the April 2008 MacWorld p.83...but it won't work as printed. Help?

Hello,
Try this.

1. Open picture, Zoom in, and resize window (enlarge) to see the entire tool bar.
2. In the toolbar, choose Instant Alpha from the Select pop-up menu.
3. Drag your mouse over a part of the background. 
Preview then selects the area you dragged over and any pixels adjacent to it that have the same colors.
4. To delete the selected area, press Delete.
To delete everything outside the selected area, choose Edit > Invert Selection and press Delete.
5. Repeat steps 2 and 3 until the image you want is left.

Thanks for the prompt reply.....the procedure you outlined seems to describe what I was attempting, but for some reason--when I expand the preview box to full screen...I do not see a choice for instant alpha, and I know I use to be able to do it.

I thought I recalled holding the return key over the "annotate" selection to see more choices...but that doesn't do it. Is it possible I have the Preview program code messed up with all my manipulation attempts?

Another other thoughts/ideas?

I did try new .jpgs to see if it was locked...but they all seem to be unlocked.

This is for a Veterans day presentation at a Veteran stand down--and now I am stuck.

Example attached of a row of ribbons I am trying to render the top R-L margins transparent:

Try this (See attachments). If you still can't see the "Select" button, go to Preview-View-Customize Toolbar and drag the "Select" button to Preview's toolbar. If you don't see any buttons or a toolbar, go to Preview-View and click on Show Toolbar.