__init__.py

# ##### BEGIN GPL LICENSE BLOCK #####
#
#  This program is free software; you can redistribute it and/or
#  modify it under the terms of the GNU General Public License
#  as published by the Free Software Foundation; either version 2
#  of the License, or (at your option) any later version.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  You should have received a copy of the GNU General Public License
#  along with this program; if not, write to the Free Software Foundation,
#  Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
#
# ##### END GPL LICENSE BLOCK #####

# <pep8-80 compliant>

bl_info = {
    "name": "Preview Addon",
    "author": "Nathan Craddock",
    "version": (1, 0, 0),
    "blender": (2, 76, 0),
    "location": "Object panel",
    "description": "Just a test",
    "warning": "",
    "category": "Object"
}

if "bpy" in locals():
    import importlib
    importlib.reload(Previews)
else:
	from . import Previews
    
import bpy
	
def register():	
    bpy.utils.register_module(__name__)
    Previews.register()


def unregister():
    bpy.utils.unregister_module(__name__)
    Previews.unregister()


if __name__ == "__main__":
    register()

Previews.py

import bpy
from bpy.types import Panel, EnumProperty, WindowManager
import bpy.utils.previews

import os

# UI
class PreviewsExamplePanel(bpy.types.Panel):
    bl_label = "Previews Example Panel"
    bl_idname = "OBJECT_PT_previews"
    bl_space_type = 'PROPERTIES'
    bl_region_type = 'WINDOW'
    bl_context = "object"

    def draw(self, context):
        layout = self.layout
        wm = context.window_manager
        row = layout.row()
        
        # This tells Blender to draw the my_previews window manager object
        # (Which is our preview)
        row.template_icon_view(context.scene, "my_thumbnails")
        
        # Just a way to access which one is selected
        row = layout.row()
        row.label(text="You selected: " + bpy.context.scene.my_thumbnails)


preview_collections = {}

def generate_previews():
    # We are accessing all of the information that we generated in the register function below
    pcoll = preview_collections["thumbnail_previews"]
    image_location = pcoll.images_location
    VALID_EXTENSIONS = ('.png', '.jpg', '.jpeg')
    
    enum_items = []
    
    # Generate the thumbnails
    for i, image in enumerate(os.listdir(image_location)):
        if image.endswith(VALID_EXTENSIONS):
            filepath = os.path.join(image_location, image)
            thumb = pcoll.load(filepath, filepath, 'IMAGE')
            enum_items.append((image, image, "", thumb.icon_id, i))
            
    return enum_items
    
def register():
    from bpy.types import Scene
    from bpy.props import StringProperty, EnumProperty
    
    # Create a new preview collection (only upon register)
    pcoll = bpy.utils.previews.new()
    
    # This line needs to be uncommented if you install as an addon
    pcoll.images_location = os.path.join(os.path.dirname(__file__), "images")
    
    # This line is for running as a script. Make sure images are in a folder called images in the same
    # location as the Blender file. Comment out if you install as an addon
    #pcoll.images_location = bpy.path.abspath('//images')
    
    # Enable access to our preview collection outside of this function
    preview_collections["thumbnail_previews"] = pcoll
    
    # This is an EnumProperty to hold all of the images
    # You really can save it anywhere in bpy.types.*  Just make sure the location makes sense
    bpy.types.Scene.my_thumbnails = EnumProperty(
        items=generate_previews(),
        )
    
def unregister():
    from bpy.types import WindowManager
    for pcoll in preview_collections.values():
        bpy.utils.previews.remove(pcoll)
    preview_collections.clear()
    
    del bpy.types.Scene.my_thumbnails
   
if __name__ == "__main__":
    register()

@BETAPANDERETA this script was written many years ago, and things have changed in Blender 2.8x and above. I may update it eventually, but I don't have time to help debug right now :(

But Blender ships with example python templates, and there is one very similar to this one. In the Text Editor header choose Templates > Python > ui_previews_dynamic_enum.py. That should get you close :)

thankyou verymuch