Dedicated scanners scan right to the edge of the glass.
All-in-one printers cannot print within a 1/4" of the edge of the sheet. As such, they do not scan within a 1/4" of the edge. This is not acceptable for this type of scanning. I have an 11 x 17 all-in-one printer and to get around this I use an 1/8" x 1/4" Evergreen Scale Models I-Beam as a spacer. Bought at Amazon. This is a nuisance, but the quality of the scans beats my CanoScan LiDE 400, and is the only scanner I use for this work.
Scan Resolution. The more pixels the more flexibility in creating quality web-size images.
Brochures, 8x10 photos, and large items are scanned at 300 dpi.
Postcard sized, are scanned at 600 dpi.
If 3" or smaller, then 1200 dpi.
Scan Quality/Size. All scanners have a quality setting. This scan will be the master file residing in the background. It can be large. Crank the setting up!
For 300 the scanner setting is to highest quality/largest size.
For 600 one step up from the default. Or at default.
For 1200 at the default.
Stitching. Source paper bigger than scanner.
No problem if the item is larger than the scanner. The scans can be stitched. Some scanners may be able to do this. I use Microsoft's free Image Composite Editor to stitch. It's all automatic. You can stitch rows of images.
The best consumer slide scanner made is still the discontinued Nikon Coolscan 5000 ED. It has 4,000-dpi true optical-resolution scanning. On eBay. Prices range. One went for cheap recently as it was listed as untested. There is an optional slide feeder. It isn't worth it. One will also need the SA-21 insert if one wants to scan film strips. One needs to be sure to get the special USB cable.
IrfanView - I first use IrfanView to losslessly rotate. Shift-J
Jpegcrop - I then use Jpegcrop to crop losslessly and split into pages. But afterwards you must clean the files with either the IrfanView GUI (Shift-J) or button on ImageUtilities tab. By default Jpegcrop saves in a non-web friendly format. And a format that the old Image Composite Editor can't read.
To get all cropped cleanly and consistently, I often will crop losslessly more than once. First with the image reduced to fit the screen, and then again with the image at 100%.