Comment by dfeng

Traditional OCRs are trained for a single task: recognize characters. They do this through visual features (and sometimes there's an implicit (or even explicit) "language" model: see https://arxiv.org/abs/1805.09441). As such, the extent of their "hallucination", or errors, is when there's ambiguity in characters, e.g. 0 vs O (that's where the implicit language model comes in). Because they're trained with a singular purpose, you would expect their confidence scores (i.e. logprobs) to be well calibrated. Also, depending on the OCR model, you usually do a text detection (get bounding boxes) followed by a text recognition (read the characters), and so it's fairly local (you're only dealing with a small crop).

On the other hand, these VLMs are very generic models – yes, they're trained on OCR tasks, but also a dozen of other tasks. As such, they're really good OCR models, but they tend to be not as well calibrated. We use VLMs at work (Qwen2-VL to be specific), and we don't find it hallucinates that often, but we're not dealing with long documents. I would assume that as you're dealing with a larger set of documents, you have a much larger context, which increases the chances of the model getting confused and hallucinating.