Of course you can if you think that neither you nor anybody else will ever need these photos again in the future.
As for me, I keep all my photos on an external hard drive, sorted by place and date, just in case. First of all, these have a higher resolution than those posted on iNat. Secondly, a backup is never amiss. Thirdly, one never knows what exactly in their photos may turn out to be important in the future, maybe some detail in the background that was not even considered worthy of a separate observation page. I suspect that 99.9% of my original photos do not actually contain any important additional information - however, I feel safe that, if I ever need that 0.1%, it is not lost forever.
Disclaimer: As a researcher by trade, I am used to keeping record of as much as possible and definitely do not recommend this way of action to everybody :)