You can display the image associated with a texture in the UV Texture Editor. The image appears behind the UVs so you can rearrange the UVs in relation to the image.
If the texture quality is poor or if parts of the texture do not display correctly, you can modify the display quality with the Hardware Texturing settings in the Attribute Editor for the material node.
If you are using a file texture, the best display mode for the Texture resolution setting is Default. (The other settings, such as High, are best for procedural textures.)
If you experience resolution or cropping problems in the texture image display, use Image > UV Texture Editor Baking to bake the texture. You must rebake the texture (using UV Texture Editor toolbar) after making changes to the texture (File node and place2dTexture node attributes) in order to see the effect of those changes.