If your graphics software is fairly new - 2010 or newer it will probably not use the TWAIN drivers anymore, so the directions I give for Acquire will not work for you.
You'll have to use the scanner's own software to grab images.
Unfortunately I found out the options with this basic software is not nearly as good as what I've been using with my older software...such is progress.

We need scans set to 300dpi and size set to 12 inches (tallest or widest point).
JPG format is what you should use.
NOTE! If the scanned image will need a lot of post touch-ups and adjustments - save the file in TIFF format initially.
If you plan on touching up the image right after you scan it, and not initially save it as a JPG file - do your digital repair...then you can save it as a JPG.
Once you save it in JPG format it is compressed - so if you make changes and repairs to that saved file and save it again - the file become re-compressed and the file will decrease in quality, slightly. If you save changes to this JPG file over and over the quality will keep degrading.
You will notice that the TIF file size will be almost 3 times the size of a JPG format, and while TIF is the better format for high resolution captures you'll have to weigh it against the extra hard drive space you will need. So one option is after you have touched up the image and made your other adjustments then you could use the SAVE AS option to JPG...then discard the original TIF file...as long as you don't plan on doing a lot more future editing of this file which will degrade during future saves.

If the picture is especially historically important and/or the original photo was in exceptionally good qualilty that gives you an excellent scanned image you should consider saving and keeping it in TIF format...BUT for most pictures that are general in nature and probably not the best quality print in the first place and also may have deteriorated some over the years - saving it as a TIF will not improve on the image and really a waste of hard drive space.

If you have scans that are higher in resolution that is OK but here is an example to use.
An image scanned at 300dpi and 12 inches by 8 inches will be the basically the same as an image scanned at 600dpi and 6 inches by 4 inches.
So if you have a 600 dpi scan but the image is only 3 inches by 2 inches that won't be something we can use.
If you have acceptable dpi and size scans but saved them in TIF format that is OK but they may be too large in file size to send as attachments by e-mail.

If your scans are larger than the minimum requirements please do not downsize them. If you have any questions please call me at 712 653-3259 or e-mail me at manningveterans@davidkusel.com