Removing the image on the left of an UISearchbar

// hide magnifying glass
    UITextField* searchField = nil;
    for (UIView* subview in searchBar.subviews) {
        if ([subview isKindOfClass:[UITextField class]]) {
            searchField = (UITextField*)subview;
            break;
        }
    }
    if (searchField) {
        searchField.leftViewMode = UITextFieldViewModeNever;
    }

This hides magnifying glass. Works well.

To completely remove the icon, you can use the following lines of code:

Objective-C:

// Remove the icon, which is located in the left view
[UITextField appearanceWhenContainedIn:[UISearchBar class], nil].leftView = nil;

// Give some left padding between the edge of the search bar and the text the user enters
[UISearchBar appearance].searchTextPositionAdjustment = UIOffsetMake(10, 0);

Swift:

// Remove the icon, which is located in the left view
UITextField.appearanceWhenContainedInInstancesOfClasses([UISearchBar.self]).leftView = nil

// Give some left padding between the edge of the search bar and the text the user enters
UISearchBar.appearance().searchTextPositionAdjustment = UIOffsetMake(10, 0)

In iOS 5.0+, you can customize the search bar image using

- (void)setImage:(UIImage *)iconImage forSearchBarIcon:(UISearchBarIcon)icon state:(UIControlState)state

in a specific instance of a UISearchBar or across a bunch using the UIAppearance proxy.