Teaching a man (or women) how to fish:
Usually Mach-O Linker Error means you have not included a header file for a function you are using in your code.
Easiest way is to copy that function or method call and paste into Xcode quick search using shift+command+O. This will search all frameworks (and header files), find that function or method call and show you its location (the header in this case):
In this case, this call belongs to the Accelerate framework so on top of your file, enter:
#import <Accelerate/Accelerate.h>
When doing quick search, you might have to get rid of leading underscore. In other words, search for vImageBoxConvolve_ARGB8888
Hope this helps