full-size images

Often an image copied from the web will appear in DTP only as a thumbnail. But if I paste it first into another app such as Apple’s Pages, it appears full-size, and I can then cop[y it and paste it into DTP where it will appear full-size.

Why is this, and how can I avoid the extra step?

Which browser do you use? In addition, an example would be helpful to reproduce/understand this.