digital still cameras
You can erase the images one at a time or all at once. Or you can simply reformat the flash card, wiping it clean.
To erase a single image while in playback mode, scroll to the image you want to delete, then press the button marked with a trashcan icon. At the prompt, use the right arrow of the omni-selector to scroll to OK and confirm you want to delete the image. Then press the SET button to delete the picture.
Rebel: To erase all images on the memory card at once, in playback mode press the Trashcan icon and use the arrow keys to navigate to "All." Then navigate to "OK" and press SET to erase all images.
PowerShot: In playback mode, press the MENU button and navigate to the blue Play Menu. Then use the down arrow on the omni selector to scroll down to Erase all... Press SET, then confirm your decision by scrolling sideways to OK and pressing SET again.
You now can go back to camera mode and shoot more photos on the erased card.
Deleting Images As You Shoot
Since images appear on the LCD for two seconds as soon as they're shot, you often know immediately when a shot hasn't worked out and can be discarded. Press the Trash Can button (at the bottom left of the camera back on the Rebel) while the image is on screen and a confirmation dialog will appear. Press the right arrow key to select OK and then press the SET button. With a bit of practice, you can get very fast at this, and not have to worry about your CF card being filled up with poor images that you'll have to weed out later. But be careful - because the LCD is small, sometimes you can't see an image clearly enough to know that what you thought was garbage actually contained something you should have kept. Be judicious with what you delete.
Re-Formatting the CompactFlash Card
Reformatting the CF card has a similar effect to using the Erase All function, with one important difference: If you've used the same CF card in an audio recorder / player or other device, the "Erase All" function simply deletes the photos on the camera. Formatting the card wipes it entirely clean, including any non-camera data on the card. If a CF card starts to malfunction, reformatting will often restore it to full working condition.
Rebel: Access the Format option from the second Setup menu.
PowerShot: Press the MENU button and then scroll sideways to select the orange or yellow setup menu. Then scroll down to the Format... line.
With Format... highlighted, press SET and then confirm your decision by scrolling sidewasy to OK and press SET again.
You now can go into camera mode and take a new set of photos on the re-formatted card.