Whenever you move or resize a frame, it will try to align itself with the edges of nearby frames; this helps you produce neatly-arranged collections of images.

This magnetic effect is felt anywhere a vertical or horizontal edge of a frame is shared with other frames.

When multiple images share an edge, then FotoFusion allows you to affect both images at the same time by manipulating that shared edge; a 'Snap' (a small draggable control) is placed on ruler at the position of the shared edge:

Dragging the snap will resize all frames that have an edge that aligns with that snap.
Dragging a snap is a quick way to resize many frames at once; it converts tedious layout problems into a trivial action.

Moving snaps using the mouse
To move a snap,

1) Move the mouse over the snap

2) Press and hold the left mouse button.

3) Drag the mouse.

All images that are affected by that snap will resize. When you are done, release the left mouse button.

You can press the 'esc' key to abort the drag if necessary.

To turn this feature off, click on TOOLS in the menu bar, choose "Editing" and uncheck "Magnetic Frames."