Winforms doesn't do that well when you resize all it's controls - it can enlarge or shrink a button or a text box for example, but it won't change the text size it uses, which can make it look a bit silly.
However, what you probably want to do is fix some controls relative to the edges or the form, and resize the image:
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becomes:
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In which case, look at the Anchor property of each control:
Image should be Top, Left, Bottom, and Right
TextBox should be Left, Bottom and Right
the two buttons should be Bottom and Right only.
Try it: you'll see what I mean.