It seems a number of people do find it difficult to get an image uploaded so I thought I'd try to write an easy to understand quick guide to cover the basics which could be expanded upon if required.
I will try to show you how I do it and this will obviously be with what I use. I have no brand loyalty or recommendations other than I have tried it and it works.
I am using Windows! Mac users may need another guide.
OK. I will try to use only free software where possible for no other reason than it is free for you to try. There are many alternatives which may work for you too.
I use an Epson perfection 3490 photo as it cost me 50p at a car boot.
It is very good though even at £50 if you had to pay that. It has been superceded by newer models.
**Info added for Canon scanners**
Requirements:
Epson TWAIN driver -
Download linkGoogle Picasa -
Download linkFlickr - Create a free account at
http://www.flickr.com/Optional
Dropbox - Create a free 2Gb account at
http://www.dropbox.com/email me for invite for free additional storage
Dropbox download -
https://www.dropbox.com/downloadingOK so your scanner is installed and working. You have downloaded Picasa and installed it. You have a free Flickr account and an optional Dropbox account for additional offline backup.
I recommend Dropbox if you are using the free Flickr account as with this there is a limit to the size of your images. They are still stored in Flickr at full resolution but you cannot access them unless you subscribe which is well worth it if you plan on scanning many images. Dropbox will give you 2Gb + a free 250Mb from me which is enough to store 100's if not 1000's of stamp scans.
By default on Windows the Dropbox 'sync' folder is stored in 'My Documents\My Dropbox'. Any file or folder you put in here will automatically be stored securely online too as a backup so I recommend this is used.
Onto the scanning.
Place your stamp to be scanned face down on the clean, clear bed of the scanner as square as possible (we will adjust this later if skewed). If you have some black card place this on the stamp and weight this down with a small book/magazine or whatever you have to hand.
Open Picasa
Click on the import button in the top left area.
In the import to box select where you want to save your images. If you are using Dropbox create a new folder in 'My Dropbox' called scans or something descriptive.
Select your scanner from the 'Import from' box.

The scanner interface (TWAIN) software should start
Epson see below for Canon

Change the mode to 'Professional'

You may not see all of the same settings but try to match them wherever possible with the exception of resolution which should be set no larger than your scanners maximum optical resolution which you can find in the specification document or online.
Click the reset button to set everything to deafult.
Now click the preview button

Drag a box around your image - Click in one corner and whilst holding the left mouse button move the mouse to the diagonally opposite corner and release.

Repeat the above selection process is scanning multiple items.
Click the 'All' button if scanning multiple images.
Click Scan. Let your scanner do its work then click Close.
Canon - This is from a Lide 20

First select professional mode - 1
Select your optimal resolution - 2
Click Preview - 3

Ensure the selection mode is enabled - 1
Draw a selection around the stamp - 2
Click Scan - 3
----
End of scanning section----
You should now have an image in Picasa.
Image editingDouble click the scanned image to go into editing mode.
You should see on the left hand side 'Basic fixes' Select straighten.
Use the slider to align your stamp with the gridlines.
When straight click 'Apply'.

I wouldn't recommend any other changes except for engraved stamps which benefit from some minor sharpening.
This can be found on the 'Effects' tab on the left hand side.
Again adjust the slider to suit your requirements.
Click 'Apply' when done.

The next step is to get our scanned image uploaded to a site from where we can share it.
So open Flickr in your internet browser and login.
Click on the Upload link

Click on Choose Photo and Videos.
Browse to where you save your scans (My Documents\My Dropbox\Scans) and select you file or files.
Your file(s) will appear in the list to be uploaded.

Click 'Upload Photos and videos'

Now wait for your images to be uploaded.
Getting your images into a forum postNow your images are in Flickr we can share them.
In Flickr click on 'You'

You should see the images you uploaded.
Choose the image you want to upload by clicking on it.
Choose 'Share this'

Click on 'Grab HTML/BBCode'
Choose the size you want from the dropdown box.
Select BBcode.
The section we are interested in is
{img}http://farm2.static.flickr.com/1111...c2f331aa.jpg{/img}I have changed the brackets from square [] in the above example so you can see it.
Paste this into your post - click preview and hopefully you should see your image appear.
There you have the basics so now get those images posted.