import bpy

def node_score(node):
    if node.bl_idname != "ShaderNodeTexImage":
        return 0

    src = input_node_for(node)

    if src is None:
        score1= 1
    elif src.bl_idname == "ShaderNodeUVMap":
        score1= 2
    else:
        score1=0

    dst = output_node_for(node)

    if dst is None:
        score2=3
    elif dst.bl_idname == "ShaderNodeEmission":
        score2= 2
    else:
        score2= 0

    return min(score1,score2)


def plausible_image(node):
    return node_score(node)>0


def input_node_for(node):
    links = node.inputs[0].links
    if 0<len(links):
        return links[0].from_node

    return None


def output_node_for(node):
    links = node.outputs[0].links
    if 0 < len(links):
        return links[0].to_node

    return None


def select_image_nodes(obj):
    mats = set()

    for sl in obj.material_slots:
        mats.add(sl.material)

    per_mat = []
    for mat in mats:
        candidates=[]
        for node in mat.node_tree.nodes:
            #print(node.bl_idname)

            score = node_score(node)
            if score>0:
                candidates.append(node)
                print([score, node.image, uv_src_name(node), output_node_for(node)])
        per_mat.append({
            'candidates':candidates,
            'mat':mat,
        })

    pm0 = per_mat[0]
    trim= keys_for(pm0)

    for i in range(1,len(per_mat)):
        x = keys_for(per_mat[i])
        trim = trim.intersection(x)

    best = None
    for x in trim:
        if best is None or best[2] < x[2]:
            best = x
    if best is None:
        raise BaseException("could not find a consistent bake image with UVmap to select in the various materials' node trees")


    for pm in per_mat:
        q = [ node for node in pm['candidates'] if node.image.name == best[0] ]
        if len(q)<1:
            raise BaseException("none of the candidates on material %r match %r"%(pm['mat'], best[0]))
        mat = pm['mat']
        print([mat, q])
        for node in mat.node_tree.nodes:
            node.select = (node==q[0])
        mat.node_tree.nodes.active = q[0]

def keys_for(pm0):
    return set([tuple([x.image.name, uv_src_name(x), node_score(x)]) for x in pm0['candidates']])


def uv_src_name(node):
    src = input_node_for(node)
    if src is None:
        return None
    else:
        return src.uv_map


select_image_nodes(bpy.context.active_object)