I use a picture in libreoffice writer in my background but need transparency to see the text
Is the picture really in background? Right-click the picture and look, whether “In Background” is active.
When your picture is already in background and you need to do something with the picture, then you have to move it temporarily to foreground. Double-click the image identifier in the Navigator and then choose “To foreground” in the context menu of the now active picture.
When the picture is active it should have green handles and the picture toolbar should be open. If not, open the toolbar via menu View > Toolbars. To set the transparency use the number field next to the wineglass icon. But perhaps transparency is not the best solution. You should try the item “Watermark” from the graphic mode drop-down list too. That generates a pale picture. Or you make such settings yourself using the color bar, located between the wineglass icon and the graphic mode list.
If your picture is not an inserted graphic object but the filling of the page, then you need to edit the picture externally and set it then as page filling again.
I worked for me
Select Image Click View dropdown. Click toolbars. Check drawing. Then bottom left corner click on Default and change to Watermark then the opacity levels are there for you to choose. It will let you change the watermark even after you set it to background once you’ve gone through this process.