Background picture fade

how to fade a picture to put in background of text message

Not directly an answer but a workaround:

Choose Format → Page then go to Area-tab and choose/import a picture. Now you can go to the Transparency-tab and set your value (may need tweaking) and then on the Page-tab you can alter the margins; zero margins means the full page is covered with your background picture - but then you’d have to use styles to recreate pseudo-margins for the text.

There are other similar explanations here, here, and Changing Page Backgrounds - LibreOffice Help.