Practice will let you decide as you start scanning. Try a few of your own photos so you have a basic idea before you attend the shindig. Use the auto scan and see what it does. You have an upscale scanner so output should e great. If photos are small, worn, scratched or torn then I select a higher resolution or increase the size so I can work on it later. I rarely use other scanner settings, relying on my photo editing software to do these things. I recently scanned a 1968 passport black and white photo of my wife at 600% of the original size, cleaned it up and printed it as an 8 x 10 and it came out quite good IMHO. DPI. What do you intend to do with the scans? I ask because a computer reads 72 DPI but if you intend to print then that is useless and will show jaggies so if I intend to print I select 300 DPI. Again, play a little and make your choices.

A fax scan may be mostly black or white dots - no shades of gray. Because of this, text comes through ok but most illustrations and color do not - those will be blobs of black. If this is acceptable, then you can use a fax machine to scan your documents. Email the scans from your fax machine to your email address, and then download the emails into your computer. Test the fax machine for duplication quality. Many fax machines default to low resolution scans for transmission savings and speed. Inrease the resolution as needed assuming your machine is adjustable. If you have color documents, use a scanner. If your documents contain graphics, but gray scale is ok, use the scanner and set the output to 256 shades of gray. (Gray scale is a much smaller file size than color scans. 256 shades of gray is adequate for duplicating most black/white photos.)

It depends on what you want to do with the scan. Your scan should be at the dpi that is correct for how you will use it. Let's assume you want to scan an old 4x5 inch photo so you can reproduce it at the same size on a modern inkjet printer like an HP Photosmart: To start you need to know the dpi requirement of the printer that will give you the printer's best result. An HP Photosmart printer will max out with an input image around 200 dpi -- the same is true for most of the major brand inkjet printers. In other words dpi above 200 in a file sent to an inkjet printer is overkill -- it does no good. (You've been scanning at 150 dpi. The difference between 150 and 200 dpi is pretty minor and most people aren't going to notice it.) So, if you want to scan a 4x5 inch photo to output on an HP Photosmart printer at 4x5 inches a scan at 200 dpi would be ideal. But what if you want to scan a 4x5 inch photo to output on an HP Photosmart printer at 8x10 inches? If you scan the original at 200 dpi you will lose half your resolution when you scale it up to 8x10 -- it will only be 100 dpi. So, to get an 8x10 inch 200 dpi file to send to a Photosmart printer you need to scan your 4x5 original at 400 dpi to account for the scaling change. You see it's a direct mathematical relationship: 5 * 2 = 10 so 200 * 2 = 400.

The answer to your question is: no. If you pick up a low res image off the internet and/or a JPG image which is damaged from compression (almost all images on WWW fit this category) then you have a fixed amount of information. There's nothing you can do to increase that amount of information. If you print the image large enough and the pixels show, you can use interpolation to increase the pixel count. This will smooth out the pixels but it does not increase the total information content. Interpolation can also further damage the information in the image. If your software allows you to increase the res of an image, it's best to make multiple small increases rather than one large increase. If you're scanning original work at your desktop and you have questions about what resolution to scan with, the link provided is a scalling/scan res calculator. Here is a link that might be useful: scan res calc