I use PicPick to do image captures in-game. PicPick is an excellent graphic manipulation and screenshotting program and is free for home use. PicPick also allow you do screen grabs of set dimensions, which I how I am able to capture multiple images with the same dimensions every time.
I also use the skin "Larger Dressing Room" which greatly increases the size of your Dressing Room and makes for much better screen grabs of armour/items.
I use the following standards when capturing images from in-game:
|Image Usage||Dimensions||Format||Naming Standard|
|Icons||32 x 32||PNG||itemname-icon.png|
|Armour Sets (whole body, elf/man)||320 x 680||JPG||armourSetName (front or back).jpg|
|Armour Sets (whole body, dwarf)||420 x 640||JPG||armourSetName (front or back).jpg|
|Armour Sets (top/bottom-half, elf/man)||320 x 400||JPG||armourSetName (front or back).jpg|
|Armour Sets (top/bottom-half, dwarf)||420 x 380||JPG||armourSetName (front or back).jpg|
When capturing images, keep in mind that the Dressing Room window background is not opaque. It does allow some of the underlying background to bleed through. Therefore you want to find a spot with a patch of ground that is very plain and dark and position your Dressing Room window over that spot before taking the screen grab.
When capturing images of armour sets, I always capture both a front-facing image (labelled armoursetname (front).jpg) and a backwards-facing image (labelled armoursetname (back).jpg). This is helpful because when players use 3rd person view, they are often looking at the back of their character, so it's helpful to know what the set will look like from behind!