Can you provide the program and the image?

Ofc, there it is ^^'

1. int DeplacementX, DeplacementY, PositionCurseurX, PositionCurseurY, PositionBalleX, PositionBalleY;
2. float Dragon1X, Dragon1Y;
3. boolean Starter = false, Dragon1 = false;
4. PImage GameBack, Curseur, Dragon;
5. void setup()
6. {
7.   GameBack = loadImage("BackGame.jpg");
8.   Curseur = loadImage("Curseur.gif");
9.   Dragon = loadImage("Dragon.gif");
10.   size(350, 475);
11.   smooth();
12.   background(0);
13.   textSize(32);
14.   DeplacementX = 3;
15.   DeplacementY = 4;
16. }
17. void mouseClicked() {
18.     Starter = true;
19.   }
20. void Nettoyage()
21. { 
22. image(GameBack,0,0);
23. }
24. void GameDessin()
25. {
26.   if (Starter) {
27.     if (PositionCurseurX > 300)
28.     {
29.       PositionCurseurX = 300;
30.     }
31.     if (PositionCurseurX < 0)
32.     {
33.       PositionCurseurX = 0;
34.     }
35.     fill(255);
36.     rect(PositionCurseurX, 440, 50, 15);
37.     image(Curseur,PositionCurseurX,440);
38.     fill(255);
39.     ellipse(PositionBalleX, PositionBalleY, 15, 15);
40.      fill(255);
41.   }
42.   else
43.   { 
44.     PositionCurseurX = (mouseX-25);
45.     if (PositionCurseurX > 300)
46.     {
47.       PositionCurseurX = 300;
48.     }
49.     if (PositionCurseurX < 0)
50.     {
51.       PositionCurseurX = 0;
52.     }
53.     fill(255);
54.     rect(PositionCurseurX, 440, 50, 15);
55.     fill(255);
56.     ellipse(PositionCurseurX+25, 433, 15, 15);
57.     image(Curseur,PositionCurseurX,440);
58.   PositionBalleX = PositionCurseurX+25;
59.   PositionBalleY = 433;
60.   }
61. }
62. //Deplacement de la balle et du dragon
63. void GameDeplacement()
64. {
65.   if (Starter) {
66.     PositionBalleX = PositionBalleX + DeplacementX;
67.     PositionBalleY = PositionBalleY + DeplacementY;
68.     PositionCurseurX = (mouseX-25);
69.     if(Dragon1=true){
70.       Dragon1X= Dragon1X+3;
71.       rect(Dragon1X,Dragon1Y,100,30);
72.       image(Dragon,Dragon1X,Dragon1Y);
73.     }
74.    
75.    
76.   }
77. }
78. void Rebond()
79. {
80.   if (Starter) {
81.     if (PositionBalleX < 0)
82.     {
83.       DeplacementX = abs(DeplacementX);
84.     }
85.     if (PositionBalleX > 350)
86.     {
87.       DeplacementX = -DeplacementX;
88.     }
89.     if (PositionBalleY < 0)
90.     {
91.       DeplacementY = abs(DeplacementY);
92.     }
93. //Rebond Coté Gauche
94.     if (PositionBalleX>mouseX-27 && PositionBalleX<mouseX-5 && PositionBalleY>437 && PositionBalleX<443)
95.     {
96.       DeplacementY = -DeplacementY;
97.       if (DeplacementX>0){
98.       DeplacementX = -DeplacementX;
99.       }
100.     }
101. //Rebond Coté Central
102.     if (PositionBalleX>=mouseX-5 && PositionBalleX<=mouseX+5 && PositionBalleY>437 && PositionBalleX<443)
103.     {
104.       DeplacementY = -DeplacementY;
105.     }
106. //Rebond Droit
107.     if (PositionBalleX>mouseX+5 && PositionBalleX<mouseX+27 && PositionBalleY>437 && PositionBalleX<443)
108.     {
109.       DeplacementY = -DeplacementY;
110.       if (DeplacementX<0){
111.        DeplacementX = -DeplacementX;
112.       }
113.     }
114.     if (PositionBalleY > 475)
115.     {
116.       noLoop();
117.       Nettoyage();
118.       text("Tu as", 100, 100);
119.       fill(0, 102, 153);
120.       text("perdu !!", 130, 200);
121.       fill(0, 102, 153);
122.      
123.     }
124.   }
125. }
126. //Fonction Je créer un rectangle (je vais mettre un dragon en image par dessus.
127. void RandomDragon(){
128.  float PassageDragon = random(1,10000);
129.   if (PassageDragon<11){
130.     Dragon1=true;
131.     Dragon1X= 0;
132.     Dragon1Y = random(0,350);
133.   }
134. }
135.    
136. void draw()
137. {
138.   RandomDragon();
139.   Nettoyage();
140.   GameDeplacement();
141.   Rebond();
142.   GameDessin();
143.   RandomDragon();
144.  
145. }

Perhaps I can't use ImageShack, but I can't get a Gif with transparency out of your link.
Note: I spotted at least one obvious error in your code:
if(Dragon1=true){
Here, you don't test your Dragon1 variable, you assign it! The test will be always true, then.
That's why I advise to use booleans as such:
if(Dragon1){
Simpler, more readable, no risk of mistake.
"more readable" if the variable shows it is a boolean, actually. Perhaps something like if (dragon1IsAlive) is better (no idea what your Dragon1 variable means, actually).

Hi!
thx for the note, i corrected it.

I create another image for the ball, and the transparency work on it. I recreated the dragon image 3 times but nothing... When i put the image on the desktop she is transparent, but not in the program... strange.

I gonne tryanother image.