This flowery background can be made this way:

1. Make a selection in an image of flowers and then choose Selections | Convert to Seamless Pattern.

2. Follow the instructions in my Semi­transparent Tiles tutorial to reduce the opacity of the tile.
   For this tile, the lower layer was filled with white and the opacity of the tile layer was reduced to 30%.

3. Save the new image.

I think this background, which is rather busy, would probably work better if its opacity were reduced even more.