usefull image functions

how to get an image path or theme a preset image ?

//output a full image
theme('image', array('path'=>'/path/to/image.jepg', 'alt'=>'my alt', 'title'=> 'my title', 'attributes'=>array('class', 'my_class_image')));
//same with an image preset
theme('image_style', array('style_name'=>'my_style', 'path'=>'/path/to/image.jepg', 'alt'=>'my alt', 'title'=> 'my title', 'attributes'=>array('class', 'my_class_image')));
 
//get an image path from an uri
$image_path = file_create_url($img['uri']);
 
//same for an image style
$image_style_path = image_style_url("my_style", $img['uri']);

Display errors - WSOD

The bootstrap override the values you could set to display error ad the reporting level. To be 100% sure everything is printed out when something fails in a blank screen (wsod), make index.php like this:

Properly render a field

Drupal offers a few (sometimes complicated...) solutions to output a field. Lets take an example with a date field.
To display the full rendered field: field_view_field()