It will store images internally if there isn't a flash card in it otherwise if there is, it will write to the card.

If you didn't have a card in, just pop one in automatically transfers them to the card.

Make sure you are putting the camera 3-4 above the base of the tree and test it out before you leave. A red light will flash on test mode when it detects something.

To compress photos, you can take them in photo programs ( I use adobe photoshop cs3) and all you have to do is decrease the pixel size and sometimes adjust the quality of the the photo depending on how big you want the image.

Hope this helps!