I unwrapped models using Blender Smart UV project (Island Margin : 0.06). After baking texture in blender render, when I zoom in and the model is big in the Blender viewport, everything is fine but when I zoom out, WHITE LINES appear on the model. I face the same issue when I export models in Unity. I also notice that these lines disappear when I uncheck Mipmap in Blender User preferences and "Generate Mip Map" in Unity. How can I fix it in Blender or Unity? Thanks
The white lines you see is the result of the downsampled MipMap versions of the textures that Unity creates for you. These are used to reduce aliasing when viewing detailed textures from distance. You should give the UV-islands more margins.