Hey bro, how did you manage to upload the photo? Unfortunately, I don't understand. Picasa is outdated, and now they suggest using Google Photos.
Hit "Upload a File" at the bottom right when you start a thread. A popup box will ask where the file is stored. If the site is running slow, a bar graph will show up in the upper right corner and you have to wait for that to stop cycling before you hit "Post" otherwise no photo will show up. Sometimes it takes awhile for the graph to go away.