>Hi,
>
>I need to scan some old pictures. The scanner I use has options for resolution starting with 200 dpi (default) and up to 4800 dpi. I do not plan to print any of the pictures. Does it then make sense to select higher resolution than 200 dpi? That is, if I select resolution higher than 200 dpi, will the resulting picture (.jpg) be of better quality? TIA.

In my experience, 150 to 200 suffices for documents (drawings, print, handwriting). For photography, I'd rather go to 300dpi, simply to preserve detail. I remember when first good laser printers came around - they couldn't do good photography until they had 300 dpi.

You can easily calculate the size of the scanned image (in pixels) - just multiply the size in inches with the resolution and you get the size in pixels. A 4x6" picture at, say, 200 dpi would be 800x1200 pixels. The actual size in bytes depends on the sharpness of the original picture, its smoothness. Any texture, including that coming from dust and cracks, is a detail that the JPEG (or other) compression will try to keep; it doesn't know it's a speck of dust. In an uncompressed format like .bmp, you can count on 3 bytes per pixel (one for each of R, G and B).