Topic: Improving Selection Tool
I had tried to make rectangular thumbnails for my photoalbum using your application.
I found some bug or at least disadvantage when using selection tool with locked H/W ratio. When you move the cursor far enough, one of the selection borders touches picture border while the other still moves so the selection aspect stops to be locked.
I also have suggestion to add function of quicker making rectangular selection when pressing CTRL or ALT or SHIFT key during selection. So without determining aspect ratio in menu.