It is still worth adding them in some cases, but if it is just a passing blurry car maybe it is not really worth mentioning.

On the site, if the image is too big, it is automatically resized (if the "automatic resize" option is checked).
If the image disappears later, it is not something automatic: it is just an admin who rejected it.

The time stamp is not required, it is just a field that you can fill when you enter the info about the vehicle. It should not be in the picture itself.
Beside the episode field there is a little "i", like for most of the fields, that gives additional details when you hover your mouse over it (or tap it if you use a touchscreen) where it explains the format of that field.