Objective-c mac application - images not displaying on other computers

Question

I recently made a mac application using objective-c in xcode, and it works fine on my computer (archiving it as an application through Xcode). But when I move it over to another computer via USB (I moved the .pkg file that I generated through Xcode - this usually works fine) the images do not display.

I checked, and when I right clicked to show the package contents of the application, the correct images were there, with the correct names. I also checked and in the Build Phases page in Xcode, the images were there correctly in the Copy Bundle Resources.

Is this a permission issue? Or is it not recognising the files for some reason?

Just to clarify, this worked on the computer I compiled it on, without extra files. All the images necessary are in the package. Also, the application was not frozen or lagging in any way I could see or notice, so I do not think it was because of a slow processor.

If this helps, the mac it worked on was a 2013 Macbook Air running OSX 10.9, and the mac where the images did not display was a 2010 iMac running OSX 10.8. The application is able to run on OSX 10.8 normally (The Deployment Target is 10.8).

When I open it on the iMac, the application just shows with the default gray background without any images, only text, buttons etc. (I am using a textured window with:

[NSColor colorWithPatternImage:[NSImage imageNamed:@"backgroundImage.jpg"]]

to have the image, as well as image wells).

Also, I am not sure if this is significant, but I went onto Activity Monitor whilst the application was running without images, and I could not see my application on the list, even with a search. (I don't have too much experience with this, so not sure if this is normal)

Thank you, any help would be appreciated.