When you scan these photos you should play around a bit first to get comfortable with the concept. Once you feel comfortable you should scan as bitmaps (.bmp) rather than jpeg (.jpg) because the quality is better. Increase the scan size so you are creating a 2 or 3 megabyte scan. Then if you wish to print or fix any tears, bends or other damage you have a nice sized file to work with. Marooma's link shows you have a flat bed scanner, great. You can set them up to scan square off the bed with that scanner. I have an HP flat bed scanner, it was given to me as mine died. But HP seem to want to control too much, hopefully you can set yours how you want it not how HP feels you should do them. (I need to get at it and see what I can really do before I bad mouth mine anymore) DO NOT scan in black and white as the results are far too stark, you will not be happy. Use full colour scanning, this is where the playing to start is so important because you can try various settings until you feel comfortable with the output. You could try duotone or greyscale just to see what it creates for you. Do you have any damaged photos?

I suggest speaking to a conservator who specializes in photographs. They may be able to recommend a method or product to fix the slides. If the slides can not be fixed, you can scan them and then fix the scans with photo editing software. I know it will not save the slides, but at least you will have the photos. And whatever you do, get them scanned before you or anyone else starts trying to clean them. Which brings me to the scanning: If you have a lot of photos that need to be scanned, it may be more cost effective for you to buy a scanner and do it yourself. You can get a very good scanner relatively cheaply and they are easy to use. You can get free photo editing software (Gimp) that has all the necessary features you need in order to fix the inevitable colour shifts and scratches in the photos, or if money is not an issue, you can get Photoshop or similar software.

what do you mean when you say that they aren't the same size? Are the original pictures different sizes? In that case, you are still ok since the slide show software will enalrge the pictures when it shows them to the screen size. Assuming you are running windows, when you open up the folder and double click on a picture, it will normally show up in windows photo viewer. If you press F11 on the keyboard or the middle button (looks like a picture) in photo viewer, it will play a slideshow of all the pictures in the folder. The slideshow should show the pictures at the same size, even if they were scanned smaller or larger.

I just discovered that I can scan a document with my smartphone. I realize that to some (most?) of you here this may be so “old news”, and thank goodness for that. You're the ones that help the rest of us out when we have problems. This post is for those, like me, who come here daily just to see what we can learn. New volunteer duties require that I scan weekly into GoogleDrive. My printer simply prints – doesn't scan or copy – so I've been researching 3-in-1 devices to give me scan abilities. Somewhere in that search a comment was made about scanning with a smartphone. That redirected my efforts and I headed to Google Play. I downloaded Tiny Scanner, took a picture of a test letter-sized document, and shared it to myself at GoogleDrive on the desktop. Scanner problem solved! There are other free scan apps available besides Tiny Scanner. In my “vast” 3 hour experience of being a user, it's working just fine for me.