Before someone else points it out, there is no such thing as a circular image, all images are four sided. You can have an "invisible" background with a GIF, but we're talking something more universal, a JPG file. The blank background is actually a white background. Although you could make some chip scans isolated on any other color if you wanted.

The reason for this is that people have asked how to make a circle crop. The easiest way is with Photoshop, or Elements, or CS4, or Corel or... you get the idea. However there is free software that won't drive you crazy trying to clean up the background.

Irfanview, you can outline and use the fill "paint bucket" and erase. Open a file in IrfanView and hit F12 and you are in IrfanPaint. Problem is you can't drag the circle around after you draw it. Here's what makes Irfanview nice. If you have an image and you don't care about having a perfect white background, you can scan a page of chips, crop one out, save-as, click Control-Z (which is go back, Irfanview step back memory is only one step!) and there's your page of chips again. You can scan a bunch at once, edit and save them, and save time.

Here's the same scan done with IrfanView, it is not a circle crop. It's quick and easy.
F12 opens IrfanPaint.
1) Click on the paint bucket, set the sensitivity to about 20 pixels. It should be set to the color white.
2) Click around the chip until you have the dark areas removed.
"F" for Full Screen
3) Select the eraser tool, erase the places that still have dark spots.
4) There's a level tool in IrfanPaint, if needed.
SaveAs (precautionary save)
5) Draw a box around the edges of the chip, you can drag them in until each side touches the chip. CTL+Y = Crop
6) CTL+U, auto color, CTL+S auto Sharpen
7) Image > Resize, set to 300 pixels, should be BiCubic and Preserve Aspect Ratio.
SAVE IT! Here's the Irfanview version, not a circle crop, just a cleaned up background

When you have chip-01, chip-02, chip-03 Etc. you open them, hit Shift-U auto color correction, Shift-S auto sharpen and save them. Irfanview also resizes and you can do color corrections manually. For free software to edit images, it's wonderful. For doing a circle crop, there are better ways.

Good News

Paint.Net is free and works. It just takes a few commands and understand what they do, and you can do some pretty easy circle crops.
Any time you make a mistake, CTL+Z is go back one step, or undo the last action if you want to call it that. If you want to save things as you work along, CTL+S is Save.

1) select the circle marquee tool. Third down on the left in the tools box.

2) Start with the cursor in the upper left of the chip, 10:30 on a clock. Drag a circle around the middle of the chip, and here's where it gets a little tricky, but makes it all very easy in the end. While still holding the left mouse button, hold the SHIFT KEY, and then you can see a circle. Shift makes the highlighted area a perfect circle, so you don't have to.
Release the Left Mouse button before the shift key. See below.

3) Getting easier, because now you look at the tools box and up on the right you see the white arrow with the +, (second down in right column)
Click the arrow and the box comes up, around your selected area. See the tiny dots, you can move the dimensions of the box, to make that circle fit the opuside of the chip. If you point to the middle of the circle you can slide the whole box around. So you make it exactly the outside of the chip and

4) Next up across the top tool bar you see "IMAGE" you click that and "CROP SELECTION" and bingo you have the chip surrounded by that checkerboard. In case you aren't familiar with layers, that's just there to show you what's invisible. You just removed everything outside of the circle that you created surrounding the chip. Everything is gone, except the chip.

But wait the chip isn't perfectly level. No problem. Up top again, "LAYERS" then "ROTATE ZOOM" (or CTL+Shift+Z) You can just use the bar on the outside of the wheel to straighten up the chip. That's nice, isn't it? You don't have to spend all kinds of time laying the chips on the scanner, in perfect alignment.

5) You want to have your scan be a nice size, so you hit "IMAGE" "RESIZE", make sure it says BiCubic and also that the Maintain Aspect Ratio is checked. For small things and downsizing, it's not going to be a big deal, but BiCubic is best in general. This one was 462 when I took the screen snapshot, the final is 300 pixels square.

6) Now Save your work. You see the checkerboard isn't there, because it only shows in the editing software, not on the saved image. Nice chip scan with an invisible circular crop.

Keep in mind the circle marquee, hold the shift key for a perfect circle, release the left mouse and then click the Move arrow, to adjust the highlighted area, or move the whole circle. Image Crop... done. The rest is pretty much intuitive and your choice if you want to color correct or sharpen or resize.

I save at Level 80 because this is the web, not fine art prints. No one is going to be printing these chip scans at 11 x 17 or full page in a magazine. 80% is a reasonable good level where you don't lose much and the file size is small enough.

Here it is, free and useful, Paint.Net http://www.getpaint.net/index.html