Hi @ANB ,
thank you for your reply.
update = Image3.Image
The original control in the edit form, when I add the image flield, form "edit files" is showed something like that

image3 has image= If(IsBlank(AddPicture1.Media), Parent.Default, (AddPicture1.Media))
in this way, when I upload the image from my PC all works and the image saved in the dataverse image field

But I need to save an image selected from a gallery (or Sharepoint Library) and not ulpload it.
If I put the image = If(IsBlank(Gallery_Carta.Selected.Thumbnail.Medium), Parent.Default, Gallery_Carta.Selected.Thumbnail.Medium) in the Image3 control the Submit(editform1) do not work and the image is not saved in the dataverse field.