Let's make your code more readable and easier to debug
$filename = "images/eventid_" . $row['event_id'] . "_images/" . $row['picture'];
$filename = rtrim($filename);
$size = getimagesize($filename);
$width = $size[0];
$height = $size[1];
Break the problem down into smaller parts:
Check $width, $height, $filename. Are they ok?
How about $row['event_id'] and $row['picture']?
Now, check $width and $height. Are they ok?
Does $filename exist on disk?
Is $filename a well formed URL? Did you switch to a funky naming convention?
Are there bad characters in there like spaces that should be %20?
Brevity isn't always the best way to write code especially when you run into ugly problems like this. My hunch is that your filenaming convention changed.