Find a plain, green background set to "Full Bright". Don't worry, we'll be getting rid of the background later. You can either use a bought or homemade photostudio (there are freebie ones out there also) or just use two modified box prims. Face east or west.
Get your look together. If it's for a portfolio then you want to emphasise your av's body...so don't make it too fussy but let your style show through.
Choose a modelling pose. Again, if it's for a portfolio, make sure your hands are away from your body and definitely not sticking into your body (trying to find these poses are a matter of trial and error...took me ages cos I've got a big arse:P).
Force the sun to sunrise or sunset, depending on how you're facing. Take pics. Save them to your hard drive. Use the camera angle tools to get multiple views of your avatar. Try different poses, try looking up or down on your av.
Use your preferred graphics editing software to open up the images. I use Photoshop. Choose an image and crop it down to the size. For an SL portfolio then 512 X 512 or 512 X 256 pixels are recommended. The game will resize everything to that anyway and other sizes end up stretched or distorted once uploaded.
Make sure that the image is in RGB color mode. To switch to RGB color mode, click on RGB Color under the Image> Mode menu.
Add a Channel Mixer adjustment layer (Layer> New Adjustment Layer> Channel Mixer). In the Channel Mixer window, check the Monochrome checkbox and set the Red to 200% and the Green to -200%. Don't close the Channel Mixer window yet!
Now drag the Constant slider towards the right until the object is a 100% white; not gray. Don't go overboard with the constant setting. If the constant is set too high, the images' edge detail will be lost.
If after you apply the Channel Mixer adjustment layer, the green areas are not completely black then select the Background layer and open the Hue/Saturation tool (Image> Adjustments> Hue/Saturation or Ctrl+U). In the Hue/Saturation tool, select Green from the Edit drop down menu and increase the saturation until the green areas turn black.
We now need to add a layer mask to the Background layer but before we can do this we need to unlock it. To do this, simply double-click on the layer and a New Layer window should appear. The default settings are fine. Click OK.
Add a layer mask to the layer we have just unlocked (Layer> Add Layer Mask> Reveal All).
Make sure the layer mask is activated. The thumbnail of the layer mask in the layers window should have a white border around it. If it doesn't, click on the thumbnail to activate the layer mask.
With the layer mask activated, open the Apply Image tool (Image> Apply Image). We'll be using the default settings in the Apply Image tool so simply click OK. When you turn off the Channel Mixer Layer, you should have your image on a transparent background.
Now that we're done converting the Channel Mixer layer into a layer mask, we can delete the Channel Mixer adjustment layer.
The image is masked, but most likely it will have green bits near the edges. To remove these, create a new layer (Layer> New Layer or Shift+Ctrl+N). In the Layers pallet, move the layer to the bottom.
Fill the bottom layer with a 50% gray. To do this, press Shift+Backspace and the Fill tool should appear. Select 50% Gray from the Use drop down menu and click OK.
With a 50% gray background, the green edges are clearly visible and the background will help us with the next step.
Select the top layer and open the Hue/Saturation tool (Image> Adjustments> Hue/Saturation or Ctrl+U). Select Green from the Edit drop down menu and set the saturation to -100. Immediately the green edge should disappear. If this is not the case then look below for the advice as to what to do with translucent fabric.
Now that we're done, choose the background you would like to use as the bottom layer. For you portfoliio, you don't want a background that will destract attention from your avatar so choose a neutral background. If in doubt then go for light grey. Also experiment with the gradient tool.
If you are wearing anything transparent then the green will probably be showing through the fabric as this will not be a true green.
Before making a layer mask, convert the channel mixer adjustment layer into a layer mask and add a 50% gray background.
You'll notice that some parts of the translucent fabric are still green. To fix this, activate the layer with the pic and use the Hue/Saturation tool (Image> Adjustments> Hue/Saturation or Ctrl+U) and select Greens from the Edit drop down menu.
Experiment with the sliders near between the two rainbow gradient bars. These sliders specify the color range that is being edited. The gray bar between the sliders indicate the the range and the outside two sliders specify faded range.Try to adjust these sliders so that the green disappears. If the colour range gets expanded, the green should disappear. Try moving the left slider towards the left slightly (so it goes into the yellow range) and if necessary the right slider slightly to the right.
Continue with the steps starting from creating a layer mask.
Now for adding some effects. Choose your Brush tool, and, with a huge brush selected, draw a blob in a secondary colour (lighter than the first, or use white) slightly off centre on your background layer.
Blur that layer. I use Photoshop, so I use the Gaussian Blur filter. You want it to blur way up into the 40-100 pixel range.
Now you have a background that looks like a lighted studio backdrop. You could also insert background images or patterns at this point... but I find them detracting for portfolio photos. The plain backdrop looks better and showcases the model better. However, take a look at Elisne Allen's flickr for great ideas on backgrounds.
Go back to top layer, the one with your av/model on it. Fix anywhere that the pose has distorted your avatar. Elbows, upper thighs, sometimes the neck ends up looking weird sometimes with some poses. You can fix this with your brush tool if you're careful... I recommend sampling the colours around the area with the eyedropper tool and lowering the opacity of your brush. Alternatively, you can use the Clone stamp or Healing brush tool. But I realize not all software has those tools. Lock the transparency of this layer (use the checkerboard icon on the layers palette in Photoshop) while you do this. Unlock it to erase into any white background left over... such as alpha hair ends or prim skirts.
Duplicate this layer. On the top layer, use the Dodge/Burn tools (or the equivalent in your software) to give the image a sense of drama. Start with a big brush and large areas of the av. Decrease your brush size, and go into the face, hands, etc. It's okay for this layer to look a bit silly and over the top.
Lower the Opacity of the top shading/highlight layer... until the lighting looks subtle and interesting.
Little things make an image stand out. Add a tiny white dot to the eyes to make them sparkle. Darken slightly the irises, nostrils, navel, etc. If you're wearing a sparkly dress, add some bling (keep it subtle!) If you really want to add your name to the image for modelling... keep that simple as well. I recommend, if you have a tablet, "signing" your name like a movie star. :) Or choose a simple font and keep the name subtle. It looks better than giant 32 point Brush Script all over the image. Add some stats if you're going to use it as a modelling card. 12 point sans fonts are fine for this.
For uploading inworld then save as a 24 bit Targa file or similar unless for some reason yu've used an alpha channel then it's 32 bit.
