Provides an abstract base class for image upload backends (e.g., Imgur, S3). It defines a common interface for uploading, handling responses, and emitting signals for success/failure. This allows adding new upload services without modifying existing tool code. The class is self-contained (only depends on Qt network) and can be extracted to add upload support to any application.

Implements dynamic positioning of tool buttons around a selection rectangle, handling edge cases such as small selections and screen boundaries. The algorithm is isolated from the rest of CaptureWidget (it just receives a bounding rect and list of buttons) and could be reused in any Qt application needing adaptive toolbar placement relative to a focus area.

A set of classes (Bool, Color, BoundedInt, KeySequence, etc.) that wrap configuration values with type validation, bounds checking, and fallback defaults. Each handler implements a common interface for serialization/deserialization and error reporting. This pattern is reusable as a generic typed configuration library for Qt applications, decoupled from Flameshot's own config storage.