The vertex shader is outputting a VS_BASIC_OUTPUT while the pixel shader is expecting a VS_LIGHTING_OUTPUT as input. The VS_BASIC_OUTPUT structure is not shown, but if it differs from VS_LIGHTING_OUTPUT that could be the problem.
I was looking around and I found an image format called SVG. from what I understand, it scales really well with any resolution. What's your opinion about it? and why isn't it replacing PNG as a file format?
Well PNG is for compressed raster/bitmapped images (i.e. a fixed resolution). I don't know much about SVG but from a cursory look, it seems to be a vector graphics format, where shapes are described with curves and such. PNG and SVG are really very different. You wouldn't want to save your raster images as SVG, as much would be lost in the translation (I'm not even sure if SVG can do raster images). Likewise you wouldn't want to save vector based art in PNG format as that would lose all the scalability.
There is software that can convert from a raster format like PNG to SVG, but I wouldn't expect the results to be very good for detailed images like what you are trying to scale.
This is really just an extension of what you are doing already.
Take all of the details that don't scale nicely (anything with sharp edges like the little cracks and nicks, the gem inlays, etc) and make each one into a separate texture (with a transparency channel). Remove all the details from the image so that what is left can be scaled using your existing method.
Then after scaling, apply all of the detail textures (with alpha blending). Taking some care to place the details appropriately on the scaled image.
nvidia-texture-tools -- for creating compressed textures
Intel Threading Building Blocks -- task scheduler for multicore processors
However, I suggest taking a look at UE4 -- for $19 (or $19/mo for continuous updates to the code) you get a complete high-end game engine with tools -- with source code to everything (except PhysX, the physics engine). It's going to be miles better than anything you'll be able to cobble together with libraries like Ogre.