1. Free Image Editor for Mac

Whenever you edit your images or photos on Mac, Free Image Editor for Mac should be the first to come in your mind. For most of us, paying Adobe's high costs will get us an app that does more than we really need or care to do. Instead, Free Image Editor for Mac handles just about every image editing task you'd think to throw at it and for free totally.

Step 1. Input Image

Once launched Free Image Editor for Mac, a window will popped up for new image creation, there you can choose the width, height, resolution, etc. for the new image. To input the local image from your Mac, click "File - Open..." and from the activated window, choose the image file you want to edit, then click "Open".

Step 2. Edit Image

At the top of the program window, you will find a toolbox which contains 14 kinds of editing tools and you can reveal any tool's options by double-clicking on its button.

Selection tool: select any area using three possible shapes of a rectangle or an ellipse
Lasso tool: select an arbitrary shape
Color Selection tool: selects all pixels on a single layer that surround a given pixel and are within a given tolerance range
Position tool: adjust the position of a layer on the canvas or scale layers and floating selections – and to rotate floating selections
Zoom tool: zoom in on any part of the canvas
Pencil: draw squares on the current layer
Paintbrush: draw various brush strokes on the current layer
Paintbucket: flood an area of similar color with a single color or texture
Text tool: place a line of text anywhere on the current layer
Eraser: erase pixels from the current layer
Color Sampling tool: set the foreground color to that of a pixel or a group of pixels on the canvas
Gradient tool: create a gradual shift from the foreground color to the background color
Smudge tool: smudge part of the current layer using the current brush shape
Crop tool: adjust the boundaries of an image so that they match a particular rectangle

Additionally, at the left bottom of the program window, you are allowed to add a new layer to this document, permanently delete this layer and duplicate the currently selected layer. You can zoom out the document view, zoom to the default zoom level and zoom in on the document view.

Step 3. Save Edited Image

Click "File - Save As..." and in the popped up window choose an output folder for the edited image file, then click "Save".

2. iPhoto

Apple's own photo management app, iPhoto, is more than enough to fix small imperfections. There are three sets of tools available: Rotate, Crop, Enhance, Red-Eye, Retouch, Collection of Effects and more complicated adjustments and so on.

3. Fotor Image Editor

For those of you out there looking for a user-friendly way to manipulate images and photos, Fotor's desktop version might just fit the bill. It doesn't have a set of tools like Photoshop for "proper" image editing (no selection marquees, no layers), but it can handle most common photo edits.