Based on what you've described, if you're looking to buy new, I'd venture that anything you buy would satisfy you. There may be some dogs at the ultra low end of the market, but for well under $600 I'd think you could get a name brand entry level laptop that would do what you want admirably. If you need storage capacity, as mentioned it's better to buy portable USB 3.0 external drives than to try to find the rare laptop with comparably sized drive, or to upgrade the laptop drive. Modern laptops are amazingly energy efficient, which benefits thing like sitting with it in your lap, and need for unrestricted airflow, as well as battery run life. If you want exceptionally long battery life, you'd have to research that, as often battery downsizing has accompanied energy efficiency. For transferring and viewing picture files or videos, or editing photos, I don't think there's much reason to be concerned that almost any new laptop is not up to the task. One thing I haven't researched of late is SD card reader speed. Those used to go at USB 2.0 speeds,. If that hasn't changed and you're impatient about such things, like me, or expect to transfer video as well, an external USB 3.0 reader is a cheap option, in which case you'll want a laptop with at least two USB 3.0 ports. Probably no longer an issue.
If you pick a smallish screen, like 12-13", I think most offerings these days will be plenty compact and lightweight. I notice and appreciate a big difference between traveling with the 12", and the 15", both in carry and in use. If you want to edit videos, that's more demanding and I honestly don't know how current entry level laptops fare. You might also appreciate a backlit keyboard under some circumstances, but those are harder to find in consumer level Windows PCs, that I've found.
If it were me, I'd buy a < 4 yr old used mid range model, with better processor and video performance, maybe screen also, for the same budget or less. Just because I might appreciate the improved speed and horsepower for some other tasks. I'd also look for backlit keyboard. I'm partial to the 4th Gen or later Intel Core processors (i3,i5,i7), just because I think they're snappier than the mainline AMD offerings, and by that era both energy consumption and integrated video performance were well enough under control in the Intel laptop hardware.