I am designing icons to include in my app and was designing them to be glossy and shiny. Then found out that app store accepts flat icons without rounded corners by doing research across internet as I did not find much information in iOS Human Interface Guidelines about icons. I would appreciate if anyone can direct me or provide me guidelines about designing icons in app as well as app icon for app store. I am completely new to this and like to know whether there are any limitations on background images and images used in the app as well.
History lesson here: Apple applied a glossy overlay and rounded corners some years ago, in their App Store. Thus, they asked that you didn't apply a glossy overlay or round corners in the App Store icon.
Nowadays rounded corners are yet applied by Apple both at the AppStore and iOS screen icons.
So:
You should not send a rounded corner icon to Apple
You May send a glossy icon to Apple. Since the reviewer is a human being and the guidelines are fuzzy, it could happen that they rejected your app because it didn't look great or trendy (the current trend is flat icons), but that is not probable.