I started to develop features for images to create layers  in Blender, as in PS and Gimp!!
A first implementation was done by KWK (Konrad Kleine)  for Gsoc2010.
Information concerning the project:
Layers v0.2.1 fixed bug for Phase 2. Completed: 14\11\2012:
1. FIX: I solved the problem of the black border around the brush.
2. FIX: Forgot IMA_IBUF_IMA in ImageExporter.cpp.
3. DEL: Deleted unused variavbles.
Layers v0.2 beta6 new features and fixed bug for Phase 2. Completed: 28\9\2012:
1. FIX: If there is only one layer and you try to delete it, Blender crashes.
2. FIX: You create a layer only if it is an image of a file or if it is a generated image.
In this way you avoid several crashes.
3. FIX: Fixed a display issue of the border around the image.
4. FIX: When you render a scene, Blender does not lock.
5. FIX: If it is invisible Baselayer and remove layers invisible, Blender crashes.
6. FIX: Quando applicavo Merge All con foto in un layer si verificava un crash.
7. UPD: When does the “Merge All” and is also deleted the “Background”, the last layer is
8. UPD: In the “Merge All” when you delete the “Background”, the “default_color” is set in
white, the property “Background” in “IMA_LAYER_BG_WHITE”.
9. UPD: Updated “startup.blend” with the properties of the dashed border to the image.
10. UPD: In the panel Image Layers when you create a layer is created with the default settings.
11. UPD: Modified functions “BKE_image_get_ibuf” and “BKE_image_acquire_ibuf” in order to allow
the integration of layers in Blender.
12. UPD: Modified “IMB_imbuf_types.h” in “DNA_imbuf_types.h”, so you can save the ImBuf within
13. UPD: Modified “image_get_ibuf” so you can return a layer or merge layers.
Useful for integration.
14. UPD: Updated Blending layers but the problem of the black border around the stroke has not
15. UPD: Changed the way you view an image in the “View” and for Render.
Now uses the “glaDrawPixelsTexScaled”.
16. UPD: In the structure “Image” is connected to ibufs the resulting image of the union of
17. ADD: Added menu “Transform”.
18. ADD: Added menu “Scale”.
19. ADD: Added “Open Image” in the header of the Space Image.
20. ADD: Ability to save layers and images in the file. “Blend”.
21. ADD: Now you can choose the layer to be used within the node “Image”.
22. ADD: Now it is possible to save an image composed of several layers.
Layers v0.1 beta2 new features and fixed bug for Phase 1. Completed: 15\4\2012:
1. FIX: Fixed many memory problems.
2. FIX: Increased the range of parameters of the function “sdrawbox” in “glutil.c”. When you
have a zomm very excessive, the dashed border of the layer changed direction.
3. FIX: Almost solved the problem of the black border, when you paint on a layer.
4. UPD: The layers are handled by the bottom to the top, as in GIMP e PS.
5. UPD: Improved UI.
6. UPD: Layer names are handled by the API of Blender
7. UPD: The BaseLayer if it is not a layer, it can not be moved.
8. UPD: Added control to manage operations on layers only when it is in the “Painting mode”.
9. ADD: Added Menu for the management of the layers.
10. ADD: Added the ability to create layers above or below a selected layer.
11. ADD: For some operations have been associated keyboard shortcuts.
12. ADD: Added the Menu “Select”.
13. ADD: Added the dotted border around the layer. With the ability to change color at the
dotted line in the Theme Manager. In addition there is also the possibility to
14. ADD: Now you see a cursor in the Image Space more inherent, which is disabled if you can
15. ADD: When you invoke the Color Sample in paint mode, you see a box at the bottom left with
the selected color.
16. ADD: Added the ability to clear a layer, even if the layer is loaded a photo.
17. ADD: The Color Picker in the Image Editor, in Vertex Paint and Texture Paint change to
reflect your choices nell’User Preferences.
18. ADD: You can add an image as a layer.
19. ADD: Added the Menu “Order”.
20. ADD: Added the Menu “Merge”.
21. ADD: Ability to lock a layer.
Layers v0.1 beta1 new features and fixed bug 2\3\2012:
1. FIX : Fixed many bugs from the patch of KWK.
2. UPD: Improved UI.
3. ADD: With the creation of a new image now you can choose the background color: Transparent, White, RGB.
4. ADD: Ability to duplicate a layer.
5. ADD: Blend Modes: Normal, Multiply, Screen, Overlay, Soft Light, Hard Light, Color Dodge, Linear Dodge, Color Burn, Linear Burn, Average, Add, Subtract, Difference, Lighten, Darken, Negation, Exclusion, Linear Light, Vivid Light, Pin Light, Hard Light.
Win 64: http://www.graphicall.org/908
Win 32: http://www.graphicall.org/909
Ubuntu 64: http://www.graphicall.org/1004
Ubuntu 32: http://www.graphicall.org/1003
MacOsx 32: http://www.graphicall.org/1017
– patch-layer Phase 2.0.rar