In practice, mainstream digital cameras are not very open in the open-source sense. Most major brands use proprietary firmware, proprietary system designs, and often proprietary RAW formats or software ecosystems, even when they also support some industry standards.

So the key distinction is:

• standards-friendly does not equal open or hackable
• using SD cards, AA batteries, tripod mounts, or a more accessible lens mount does not make the camera itself open

If your goal is an open-source-style device that you can modify or extend, consumer cameras generally are not that. If your goal is simply to maximize use of common standards, then you can favor cameras with:

• SD/SDHC storage
• DNG support
• standard tripod threads
• non-proprietary battery options where available
• lens systems with broader third-party support

But no major camera brand is especially open overall; most are built around proprietary systems intended to keep you within their ecosystem. In short: you may find cameras that support more open standards than others, but you are unlikely to find a truly open digital camera platform among mainstream models.