在Android端，可以通过将图片转换为圆形或圆角矩形来实现：

public static Bitmap getRoundedCornerBitmap(Bitmap bitmap, float roundPx) {
    Bitmap output = Bitmap.createBitmap(bitmap.getWidth(),
            bitmap.getHeight(), Config.ARGB_8888);
    Canvas canvas = new Canvas(output);

    final int color = 0xff424242;
    final Paint paint = new Paint();
    final Rect rect = new Rect(0, 0, bitmap.getWidth(), bitmap.getHeight());
    final RectF rectF = new RectF(rect);
    paint.setAntiAlias(true);
    canvas.drawARGB(0, 0, 0, 0);
    paint.setColor(color);
    canvas.drawRoundRect(rectF, roundPx, roundPx, paint);

    paint.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));
    canvas.drawBitmap(bitmap, rect, rect, paint);

    return output;
}

在iOS端，需要对UIImageView进行圆角处理：

imageView.layer.cornerRadius = imageView.frame.size.width / 2;
imageView.clipsToBounds = true;

这样就可以在两个平台上都进行圆角处理啦。