https://bugs.documentfoundation.org/show_bug.cgi?id=112195 was closed but without the whole solution.
It is not possible to have a fullpage image as background
Having a full page image as background of the whole page
User Profile Reset: No
Setting to new, https://bugs.documentfoundation.org/show_bug.cgi?id=112195#c17
*** Bug 125713 has been marked as a duplicate of this bug. ***
Just a note: it's possible, but only in tiled mode, possibly requires setting proper image width and height (so that it fits once in both directions). In "Custom position/size" and "Stretched" modes, the image still only fills inside margins.
Versión: 126.96.36.199 (x64)
Id. de compilación: 057fc023c990d676a43019934386b85b21a9ee99
Subprocs. CPU: 8; SO: Windows 10.0; Repres. IU: predet.; VCL: win;
Configuración regional: es-AR (es_AR); Idioma de IU: es-ES