Hi Eddie,

I don't know what camera you use so I'll use a 8mp camera example using Adobe Bridge & CS2.
Alamy want you to have a 48Mb +  file as your finished original.  It should be an 8 bit file as they do not accept 16Bit. It has to be in Adobe RGB 1998 colour space.

Camera.
Set your camera to shoot RAW images.
Set your camera's colour space to Adobe RGB 1998

**Computer.
**In PS CS2 set your colour working space to Adobe RGB 1998 (Under colour settings)
In ACR set you convert workspace to Adobe RGB 1998 and turn off auto sharpening (Under preferences)

Now you are ready to start shooting stock images. 

Process the RAW file through Adobe Bridge and ACR convert the RAW file to a 16bit Tiff in the Adobe colour space.  Do as many adjustments as you can in ACR to get the image as near as it can be to the finished article. Then convert and the image will open in CS2.   

Now resize the image using 'image size'. Change the pixel nomination to percentage and change 100% to 150%. Click OK.   Check the file size is as wanted.
(The 150% figure is an approximation that will work consistently well with a Canon 20/30D  you may have to use a little more or a little less depending on image and camera used) 

Make any final adjustments to the image.

View the image at 100% and carefully go over it for any dust marks or imperfections and use the clone/healing tools to remove them.  Alamy will not accept any images that are not top quality so do this thoroughly.

Finally when you are happy it is the best you can produce convert the image to 8 bit (under mode).

Save the file. This is your 48Mb+ file.  

They want a Jpeg of this file so also save as a copy using the jpeg extension.  A window will appear asking you what quality and the level must be at 10 or above. 

hth
 

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html