Item with custom texture doesn't work

You should probably do some research, but I think that a Lectern is a 3D Model, not too sure though.

lightning_rod is a 3D Model and work using texture

Your resourcepack does not have a model (inside models/item), not a bug. Check the Minecraft Wiki for more details.

To be more specific: the Model Definition (items/lectern.json) of the lectern is pointing to an item Model which does not exist (it is pointing to models/item/custom_picture.json). 

@santohyj123 i added models and now it's working, thanks

models/item/custom_picture.json

{
  "parent": "minecraft:item/generated",
  "textures": {
    "layer0": "minecraft:item/custom_picture"
  }
}