How to mark an image?

Question

How can I place a mark, like a cross-hair (to suggest "X marks the spot") and a text label associated with it, at a particular position on an image (mine in particular is Colorized)?

Answer 1

This is a simple way:

Show[
    Plot[Sin[x], {x, 0, 2 \[Pi]}],
    Graphics[{PointSize[Large], Red, Point[{3 \[Pi]/2, -1}],
    Black, Text["Minimum", {3 \[Pi]/2, -.8}]}]]

Edit

If you have an image created with Colorize you can apply the same method. In the example below img is the image you obtain by taking the first example given in the Help under Colorize.

Show[
   img,
   Graphics[{PointSize[Large], Red, Point[{20, 100}],
   White, Text["California", {30, 90}]}]]

Answer 2

Another approach:

anXtoMarkTheSpot = Graphics[{
  White,
  Line[{{0,10}, {0, -10}}], 
  Line[{{-10,0}, {10, 0}}], 
  Text[Style["the Spot",14, Bold, White, 
      TextAlignment->Left],{20,5}]}, 
  ImageSize -> 80];

treasureMap = Colorize[ExampleData[{"TestImage", "Aerial2"}]];

ImageCompose[treasureMap, anXtoMarkTheSpot, {60,40}]

Answer 3

You can also use the Drawing Tools palette to annotate an image interactively. It can be invoked in three ways:

1. Selecting Drawing Tools from the Graphics menu
2. Using the short-cut Ctrl+D or
3. Using the right-click context menu on a graphics object:

For a detailed tutorial on the Drawing Tools palette see Interactive Graphics Palette. The following image from the tutorial summarizes the functions in the palette:

Usage example: palette states and before and after appearance of the image using the same image in vucko's answer: