# Parallel Regions and Images as Links Versus Tags

Parallel regions allow multiple blocks to be executed at the same time. This adds complexity, as different blocks can alter the image data or coordinate space from different threads, which can result in errors being thrown (seemingly at random). Due to this complexity, there are two different ways that image data can be passed into a Parallel region:

1. When an image is linked into a Parallel region, it will result in the image being duplicated (aka cloned). Cloning has a slight overhead, so for very fast image processing operations, it may be faster to process sequentially. By using a link, the image will be fully cloned (pixel data and coordinate space tree), so each block will be acting on the image data independently.

   Cloning an image means that the Tool Blocks will no longer be acting on the same object, so information cannot be transferred between them. The data will need to be correlated by the user after exiting the Parallel region.

   Note: You may also need to join records from the separate images into one record.

2. If an image tag is used as input for multiple VisionPro Tool Blocks within a Parallel region, Designer will automatically prevent parallel executions in an attempt to prevent cross-thread exceptions from occurring by locking the image to one block at a time.

   When using a tag to pass image data, the same image object will be acted on by all of the blocks in the region. However, this means that the blocks may not run in parallel, since one block waits for another to finish processing on the image tag.