Have a photo and you want to change the transparency with out altering the original file?
Using Adobe Illustrator, you can use an Opacity Mask to, lets say, fade the photo image to white.
An opacity mask is essentially like a mixture of a clipping mask and a layer mask at the same time. in other words, you can use an opacity mask to control the appearance (transparency of a shape) using, in most cases, a black to white gradient. Because you can’t fill an object in Illustrator with a gradient that has transparency, we can use a mask to take away all of the areas covered by the black part of the gradient (or gray in some cases). There are many uses, which I’m sure you will discover rapidly on your own, and soft opacity gives illustrator a whole other dimension to work with.
An “Opacity Mask” refers to a mask in Illustrator that you place over an existing shape that controls its transparency based on the values of black and white in the mask. White being visible, black being transparent, and all shades of gray are in between on the opacity scale.
For the complete guide to Opacity Masks, visit the Adobe how-to here >