Before the development of computer software to aid picture manipulation, designers were known to use two L-shaped pieces of black card to visualise a picture crop. The two shapes could be placed over an illustration or photograph to create a moveable frame. The cards were then easy to move in unison to create an area to focus in on - or a crop. Imagine the movie director visualising a frame with their hands on the set of a film - it is the same principal that designers and editors apply to still photographs.

Thankfully, we have come a long way in a short space of time and PowerPoint 2007 now comes with built in cropping control so all your cropping instructions are calculated automatically with the click of a mouse.

PowerPoint 2007 gives us the tools to easily edit and enhance pictures for our slide shows that would only have been possible previously by using a professional design package. With PowerPoint 2007 you can now easily edit pictures to a high standard - all within the same program, saving you time and giving greater control over how your presentation looks.

Now you can take time to really think about the treatment of images and not just which image sits best in your presentation. Instead of simply inserting an image and resizing to fit the area on a slide, you can also control how much and which part of the image you think looks best in that area.

Most people think that cropping involves reducing or enlarging an image in proportion to the entire object. But cropping deals with how to focus in on only part of the image that you require and make that part the subject matter. With the use of clever cropping, the subject matter can be better highlighted and any boring or unnecessary aspects can be edited out of the frame.

It's easier to imagine cropping as looking at an image on a CCTV screen, then focussing in and magnifying only a small part of the image. Cropping edits out the other parts which might be irrelevant or unnecessary.

The Crop tool is located on the right side of the Format tab. When you click on the Crop tool, crop handles will appear in a dark, broken border around your picture. Think of these as representing the black L-shaped cards of yesteryear! You can now drag these handles to remove the excess elements that are unnecessary in the picture.

By cropping into an image - and cropping out any unwanted areas - your image will deliver greater impact. The viewer will be drawn to the subject matter and will not have to fight to subconsciously edit out any of the other elements in the picture that just don't need to be there.

Think of how images are effectively used in banner advertising on the web, for example. The use of shape and composition greatly add to the overall feel. The professional web designer will select an image which best suits the shape of a banner and will also crop in to better highlight the subject matter within the shape.

Cropping can help liven up the dullest images; even simple head and shoulder shots of personnel can be cropped to focus in on the eyes or take out a dull background. Consider displaying a picture portrait in a landscape shape - but do not over stretch the image to fit the space. This would add interest and excitement to the shot. If you have a series of people images which must be included in your presentation, then treat each image in the same way to give a fluent feel. Pay attention to how much space is around the subject matter, the area you will crop in to, and make the subject of each image the same size - a uniform, but more interesting, presentation is easier on the viewer.

So remember, don't think of cropping as resizing - it's a tool to really help home in on an image and produce a different treatment.

Once you have cropped your image, use the Shape Height and Shape Width tools in the Size command to enlarge or reduce the new image area to get even greater effect. The Size tab arrow also allows control of Alt Text (alternative text) which includes Web option control.

And PowerPoint 2007 also enables you to control other elements of your picture including brightness, colour control and shapes. The Picture Styles group contains a gallery which provides an array of different preset styles for use with images. For many of these options, resting the mouse over a selection will offer you a preview of the available choices.

To save struggling to align images with graphics such as arrows, it's sometimes best to abandon the mouse and use the Shift Arrow Key and then the Control Arrow Key for pixel by pixel movement. You can display a grid to help you get the image to the exact position you prefer on the slide if this helps.

A quick word about backgrounds: there's no point spending time editing your image to give maximum impact if you don't then consider how it will look with the other elements on the page. Think about the background colour and how it is going to work with coloured text or an image. Usually a white screen is too bright and the contrast between the darkest and lightest areas of the screen may be too contrasting. However, a dark coloured slide also creates problems: the contrast between the background and text is often too much for comfortable viewing.

Understanding some basic colour psychology is also useful. Certain colours can produce advancing or recessive effects, and reds appear closer to the viewer while blues appear to stand back. A simple background texture can add interest without competing with the text and images. Think also how a frame can help distinguish and lift an image from a similar coloured background.

Of course, there are many more professional picture treatments available at your fingertips in PowerPoint 2007, including compressing pictures in order to decrease the size of the files, and organising all images and image groups on your slide for easier modification.

To find out more about cropping and other picture treatments, it's wise to invest in professional training so that you can learn about all the picture tools available and how to use them to maximum effect.