Uploading photograph to replace background

Hi, I am new to Webflow and I am trying to create my own website. I want to customise the design, so I decided to use some of my own works. Once I upload the photograph and choose it as a background, the background appears empty. But this issue seems to be affected only by the photograph which I uploaded, it I use a stock image from Webflow it seems to work fine. Any suggestions on what I might be doing wrong?