Image size.

You can resize image element in pixels or percentages.

Buttons size1, size2 reduce and increase image size in two times.
Checked flag Keep aspect ratio recalculates height when you change width and visa versa.

Note: when you change image size the file of source picture is used. If this file was displaced or removed, then the stretched image saved in the project is taken: in this case each following image shrink/stretch operation will make image worse.