Once you have scanned a coin, upload it to whatever web space your ISP may provide, then go to that space and find the scan. Determine its address or URL. The address might be something like www.mydomain.com/me/scan.jpg

To post a hypertext link to the scan, use:
<a href="http://www.mydomain.com/me/scan.jpg">Click Here to see my scan</a>

To insert the scan into a web page, use:
<img src="http://www.mydomain.com/me/scan.jpg">

My scanner is a UMAX Astra 1200S - Its official resolution is 1200 x 600.  That means the "official" resolution is 1200 DPI (or dots per inch) vertically and 600 DPI horizontally.

Realistically, it means the maximum optical resolution is 600 DPI.  You always take the smaller of the two numbers in the "official" resolution.  The software can interpolate the 600 DPI and imitate resolutions up to 9600 DPI and beyond, but you will get no additional detail.

Scanners seem to do best in specific multiples of 75 dots-per-inch, or DPI.
Below are some color-adjusted scans (24 bit True Color) of a buffalo nickel.  You sometimes get weird patterns or colors in DPI that are not multiples of 150, such as 400 or 200.

75 DPI (Dots per Inch)

150 DPI (Dots per Inch)

300 DPI (Dots per Inch)

600 DPI (Dots per Inch) - This is the highest optical resolution of my scanner.

 

1200 DPI (Dots per Inch) - Interpolated (looking a little fuzzy)

And 2400 DPI (Dots per Inch) - Interpolated (Looking a LOT fuzzy)