Of the three main picture formats here is a little info on each:
.png is the web standard as they are "portable network graphic" files. They retain the pixel data as bitmaps do, however, receive the added benefit of compression to help ease download for those with slower connections.
jpg's do not retain pixel identity when saving. General colors are assigned in areas to help create a smaller files size and smoother image.
bmp's have no compression and contain all pixel data creating large file sizes. On the web this leads to longer download times and increased bandwidth usage which slows network traffic for the hosting server.
Think outside the box.
To go on an adventure, one must discard the comforts and safety of the known and trusted.