You can delete photos from the app (on the iPhone, tap on the image and then click Remove; on the Android, tap on the image, click Menu and then Delete Photo) and from the website from the check-in detail view. When you click on the photo icon from your user history or from the homepage at foursquare.com, you’ll see a larger version of your photo, and you can click the Delete button on the bottom right (the Delete button will show when you mouse over the image). When the pop up asks if you want to delete the photo, select Ok.