Q:

How I can define the edges?

I have made a code for scrolling a background in Cocos2d to create an effect of a camera, but I cant prevent the camera going beyond the edges of my background. My background is an image that is 1440*1080. My code is:
+(id) scene

{
    CCScene* scene = [CCScene node];
    TileDemo* layer = [TileDemo node];
    [scene addChild: layer];
    return scene;
}

-(id) init

{

    if ((self = [super init]))

    {
        self.isTouchEnabled = YES;
        CCSprite *Nivel1 = [CCSprite spriteWithFile:@"Nivel1.png"];
        Nivel1.position = ccp(0.5f, 0.5f);
        [self addChild:Nivel1 z:0 tag:1];
    }

    return self;

}

-(void) dealloc

{
    [super dealloc];

}

-(void) registerWithTouchDispatcher

{

    [[CCTouchDispatcher sharedDispatcher] addTargetedDelegate:self priority:0 swallowsTouches:YES];

}

-(BOOL) ccTouchBegan:(UITouch*)touch withEvent:(UIEvent*)event

{
    return YES;
}

-(void) ccTouchEnded:(UITouch*)touch withEvent:(UIEvent*)event

{

}

-(void) ccTouchCancelled:(UITouch*)touch withEvent:(UIEvent*)event

{

}

-(void) ccTouchMoved:(UITouch*)touch withEvent:(UIEvent*)event

{
    CGPoint touchLocation = [touch locationInView: [touch view]];
    CGPoint prevLocation = [touch previousLocationInView: [touch view]];

    touchLocation = [[CCDirector sharedDirector] convertToGL: touchLocation];
    prevLocation = [[CCDirector sharedDirector] convertToGL: prevLocation];

    CGPoint diff = ccpSub(touchLocation,prevLocation);

    CCNode* node = [self getChildByTag:1];
    CGPoint currentPos = [node position];
    [node setPosition: ccpAdd(currentPos, diff)];
}

@end

A:

you have to calculate maximum and minimum posiible position of your sprite and check it in your touchMoved:withEvent: method. On my mind, it is easier to calculate these values, when anchorPoint of your sprite is in (0.f, 0.f), instead of standard (0.5f, 0.5f). then your positions will be
CGPoint maxPos = ccp(0.f, 0.f);
CGPoint minPos = ccp((spriteWidth - screenWidth) * (-1), (spriteHeight - screnHeight) * (-1));

then just check if your sprite's new position is in valid range before set it.

