Assuming you would like to add background images to the pose stand (pose stand backdrops), on your Wardrobe web page, open the "Choose Posestand Backdrop" window:
Tools > Posestand Backdrops > Texture,
then click on the "Add Backdrop" button, and enter the UUID of the texture you'd like to add and assign it the appropriate tags.
To apply a backdrop to the inworld pose stand, simply click the thumbnail image in the "Choose Posestand Backdrop" window.