I run a photo studio in London, and I was looking for Mac software that would enable me to make a semi-transparent floating window on my computer. I wanted to be able to open any image to use as a floating positioning guide over the actual image that I'm shooting.
I use Adobe Lightroom, and I wanted to be able to float the art-director's layout over my photo in Lightroom, to check that my shot was a good fit. Sometimes I wanted to put another element of a composite over my image to check position and perspective, or I wanted to have an image visible over my Lightroom capture so I could match it.
I couldn't find any software to do this, so I wrote it myself: Overlay for Mac is the result. It works with Lightroom, Aperture, ACR or any OS X software.
How to use Overlay
Drag the Overlay application icon to your Applications folder. If you want Overlay to appear in your Dock, drag it from your applications folder onto your Dock.
Open an image
Drag an image file onto Overlay, or onto Overlay's Dock icon, or choose File > Open from the menus, or click the "Open..." button in the Overlay Control Panel. Overlay can open almost all types of image file, including RAW files from all the cameras supported by Mac OS X, and it can open PDFs.
Rotate, scale and position it.
The Overlay window can be resized and positioned like any normal window, and the controls in The Overlay Control panel (which can also be repositioned) enables you to scale (resize), rotate and position your image within the window. You can also control the opacity of the main window, and show or hide it as required. The Overlay windows continue to float over ALL other windows on your Mac unless you hide the main window, reduce its opacity to zero, or quit.
You can also reposition the overlay image by holding down the SPACEBAR while you mouse over the overlay image window (like in Adobe Photoshop). To control opacity in the main window hold SHIFT while mousing. To rotate the image in the main window hold down COMMAND(APPLE) while mousing, and to scale (resize) the image in the main window, hold ALT while mousing. The image can also be positioned using the arrow keys.
Switch on and off, or replace the image
You can switch the Overlay image on and off by using the Show/Hide button (you can also reduce the transparency to zero or increase to 100% using the Opacity slider, to get the same effect). To replace the image in the Overlay window, just open a new file.
Overlay behaves slightly differently to other Apple applications because its windows are ALWAYS visible (otherwise they would not be much use). If you have clicked on a background application and you want to get BACK to Overlay, just click on one of its windows.
Keyboard shortcuts and menus
Hide or show the main Overlay window using the Window>Hide menu, or the shortcut key CMND-H. You can also hide the Overlay Control Panel using CMND-K, or from the Window menu. For other leyboard shortcuts, see their menu items. Be careful when you have BOTH Overlay and Control windows hidden - you need to have the Overlay application active (check in the menu bar) to be able to make either of the windows visible again.