Background

[Adam Christian5E5D]

Just wondering why when I have removed the background from an image when I paste it into illustrator and photoshop in then comes up with a big black background around the image. I used to be able to copy and paste the image in no problem then the next time I tried a big black background appeard with the image. Please help 

[Adam Christian5E5D]

Images with no background when put into illustrator come up with a black background. Why?