Regardless of whether you scan photos yourself or use images that someone else has scanned, it's important that you understand the scanning process and the appropriate specifications for your presentation medium. Even if someone else scans the photos for you, by not asking for the right image specification, you might receive a 3MB "brick" instead of a manageable 30K file.

TWAIN 
TWAIN is a standard interface between image processing software and a scanner or digital camera.  Most scanners sold today come with TWAIN drivers,  a photo-editing application, optical character recognition (OCR) software, and some type of color calibration tools.  When you initially launch your scanning software, you can set up the image-editing software, such as Photoshop, to always display the TWAIN image capture window. 

Resolution
The first thing you need to consider before scanning an image is the resolution you'll need.  In order to determine the resolution at which to scan an image, you need to know how you plan to display the final image.  For screen display, scan at 72 ppi for photographs; 120 ppi for line drawings or images with small text.  For printing, scan at 300 ppi.

Scan Only What You Need
There's no use in scanning a large area when you know you'll only be using a small portion of the page. You can keep your file size down if you preview the scan and then select only the area you're going to use. This will also save you valuable time.

Cover the Scan
If the item you're scanning is on thin paper with text or graphics on both sides, you scanner my pick up all of one side and part of the other with a single scan. While you could look at this as a time saver of sorts, the resulting image doesn't turn out looking too acceptable. To overcome this problem, keep a piece of black construction paper handy. Cover the document with the black paper before you scan it to prevent the bleed-through from occurring.

Save As A Native
When you create a scan, always save it in the native format of your image editing software - such as a .PSD format for Photoshop. This will reduce any image loss possible when you convert the image from one format to another. It will also save you time.

After the Scan
After you've imported or placed a scanned image in your bitmap-editing software, you can take some specific steps to create the highest-quality image with the smallest optimal file size. Keep in mind that the speed at which your editing software will perform these tasks is often directly related to the amount of RAM on your computer and the available hard-disk space for the software to create additional working memory for larger images.

Rotate the Image
First, it's a good idea to orient the image correctly, so look for the ROTATE command in your editing software and use it. Don't worry: The image will not degrade as a result of rotating.

Crop 'Till You Drop
Second, good image composition dictates that you remove nonessential elements by cropping them out of the picture. Distracting background elements or wasted space can cause your audience's attention to wander around the image, as opposed to focusing on the important elements. Stock-photo images will often show the dirty outside frame of the 35mm slide from which they were digitally created. Also, the proportions of the crop should reflect the composition of the space into which you will be placing the final image. In a particular presentation slide, you may have text on the left and need a square or vertically oriented image on the right. Here's your chance to create it.

Adjust color, brightness and contrast 
Images scanned from color transparencies frequently have too much contrast, with blue color-shifts characteristic of Ektachrome film. Some software will provide previews of color, brightness and contrast adjustments to help you correct this problem. For example, Photoshop provides a VARIATIONS option under the IMAGE > ADJUST menu item. Those who struggle with color theory will find it much easier to make color, contrast and brightness decisions from thumbnail previews rather than endlessly moving up and down slide bars.

Sharpen images
If you're significantly increasing the image's size when you scan it, the resulting image may not look as sharp as the original. To combat this, use the sharpening command in your software. In Adobe Photoshop, the FILTER menu provides an UNSHARP MASK option that adds contrast to adjoining pixels in degrees that you can control. Be aware, though, that over-sharpening an image can make it look unnatural and pixilated. Try to find a good balance.

Eliminate imperfections
When we start fixing such image flaws as eyeglass reflection, red eye and unwanted telephone poles, the real fun begins. The "fun," however, will require that you experiment a bit to master the tools. Still, it's quite a kick making a good photo look great. Photoshop's rubber stamp tool allows you to sample adjoining pixels and reproduce them so you can eliminate small problems. Using the stamp tool, you should be able to easily fix some things, such as a sky background, but you'll need more practice to be able to remove a stray hair across someone's face. It can be done, though.

Interpolate via the Software
The physical resolution at which a device can capture an image is known as optical resolution. The term is used most frequently in reference to optical scanners and digital cameras. You will also hear it referred to as native resolution.  In contrast, the interpolated resolution indicates the resolution that the device can yield through interpolation -- the process of generating intermediate values based on known values. For example, most scanners offer a maximum optical resolution of only 600 dpi, but an interpolated resolution from 1,200 to 9,600 dpi.

Although many of today's scanners allow you to interpolate resolution far above their optical limit as  you scan your image (part of the user-modified settings on the TWAIN input window),  your images will be crisper if you will instead use a good image-editing program such as Photoshop to perform any interpolation after you have scanned the image at maximum optical resolution.  The same is true when you need to down-sample to a lower resolution. Let the program do it for you, not the scanner.