Incorrect texture in 3d model loading using ASSIMP & OpenGL

I've found the workaround. I changed how to access textures in recursive_render function using the following code :

glTexCoord2f(mesh->mTextureCoords[0][vertexIndex].x,  mesh->mTextureCoords[0][vertexIndex].y);

instead of:

glTexCoord2f(mesh->mTextureCoords[0][vertexIndex].x,  1-mesh->mTextureCoords[0][vertexIndex].y);

This is not a problem with textures. Your problem is coming from backface culling (at least it seems like it since you can kind of see inside the duck). Either your polygons are wound in the wrong order, or your backface culling is set up incorrectly. If you post the code where you set the backface culling, we can see exactly what is wrong.

There could also be the possibility that some of your normals are facing inwards (which can also result from polygon winding). That would explain why your duck's beak is pitch black.