Scanning a graphic and enlarging same

Image Capture will scan. However, there are so many different ways to interpret "enlarge it" that I'm not sure what you want. Although Preview will let you open images that you have scanned, note that any real graphics manipulation will require other tools than what come pre-installed on your system. If you let us know exactly what you want to do with the scanned image, we can tell you how to accomplish that.

What scanner do you have? The software that came with the scanner should allow you to enlarge or reduce the image.

Vuescan is an excellent scanning utility, and inexpensive too. I use it all the time. You can change all sorts of characteristics of the original when you scan with it. It works with most scanners.

For more sophisticated work, Photoshop Elements 8 for Mac is a very good program; it integrates with most scanners.

Also, when you do File > Print you can scale the image when you print the document.

Well, that still isn't really a good description of what you meant, although the mention of stained glass leads me to believe that what you want is to print it larger than the original... is that correct? If so, you can scan with Image Capture, then print the image using Preview. In the print dialog, just change the Scale setting.

Enlarging an image happens one of two ways: Either by using a vector-generated graphic, or by lowering the resolution. Scans are not vector-generated, so if you want to enlarge a scan, you should scan at a higher resolution than you need for the quality of output you want, and then set the output for the size that you want. So if start with an image at 100% and you want the image to be 300 dpi or better at 150%, your scan should be at least 450 dpi.

For a stained glass project, the resolution probably does not need to be so high, and most scanners will scan at a high enough resolution that the results will be adequate unless you are multiplying the size quite a bit.

Your biggest problem may be that if you start with a letter-sized image, you may need a large-format printer to print the result.

If your printer can handle it, all you need to do is to print the image at 150% (to use your example) to enlarge it. Some all-in-ones can do that sort of enlargement when they copy, so no computer would be necessary.

Graphic Converter can do that.