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The content extraction has some limitations (see https://docs.microsoft.com/en-us/azure/cognitive-services/computer-vision/concept-recognizing-text). In particular, be aware of the following limitations:
Supported file formats: JPEG, PNG, BMP, PDF, and TIFF.
For PDF and TIFF files, up to 2000 pages (only first two pages for the free tier) are processed.
The file size must be less than 50 MB (4 MB for the free tier) and dimensions at least 50 x 50 pixels and at most 10000 x 10000 pixels.
The PDF dimensions must be at most 17 x 17 inches, corresponding to legal or A3 paper sizes and smaller.
If an error occurs, an error message will end up in the CognitiveServices.error queue in RabbitMQ. You can retry the content extraction by moving the failed message to the CognitiveServices queue.
There is a cost associated with extracting contents from files. Please see https://azure.microsoft.com/en-us/pricing/details/cognitive-services/computer-vision/ for more details.
If the extracted contents are included in freetext searches, they are searched on equal terms with the asset titles. Thus, it might be more difficult to find an asset by title.
Each time an asset is published or republished, its contents are extracted again.
Repopulating search caches and assets might take significantly more time if content extraction has been enabled.
Freetext searches might be slower when asset contents are included. However, we do not expect this to be significant.
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