We are going to import a simple binary image bitmap into EAGLE. You probably need to convert your image to get it into this format. First open it up in photoshop. Go to Image > Mode and select Grayscale (if bitmap is available you can select that now and skip the next step).
Make Bitmap 2
Now that the image is grayscale you can convert it to a bitmap. Again go to Image > Mode and now select Bitmap.
Now input 200 for the pixels/inch (DPI) you can go higher if you want better resolution, but it wont work at every fab house. Photoshop has several option for how to convert grayscale images into bitmaps. The simplest is 50% threshold which will just take everything lighter than middle gray and make it white and everything darker and make it black. Or you can select one of the various dithering algorithms they provide. Custom Pattern gives pretty cool results.
Now Select File > Save As... and make sure you save your bitmap as 1 Bit depth in Windows file format.
Ok so you want to add you own images onto your circuit boards... Here we go. Open up your library and click the package button and you will see all your packages listed. At the bottom of the list it says new and there is text field. In this text field put the name you want for the silkscreen bitmap you are going to make. Then press OK.
Enter Package Name
Type the name you want for your silkscreen bitmap and press OK.
Say Yes at the create new package prompt. Now select File > Run... from the EAGLE menu.
Within the ULP folder of the EAGLE application select the file import-bmp.ulp. Then click Open. Say OK at the prompt.
Select Your BMP
Now navigate to wherever you saved your BMP file from photoshop or GIMP. and click Open.
Choose white as the color. Unless you want the white part of the bitmap to show up as white on the silkscreen, in that case select black.
Now select DPI for Format, Inch for the Unit and 200 for the Dots Per Inch (DPI) you can select higher amounts for some fab houses but if you want pretty purple PCBs from OSH park
stick to 200. You can play with you DPI amount to make your silkscreen bigger and smaller and more or less detailed. High DPI will be smaller and more detailed. For start layer enter 21. This is the TPLACE layer in EAGLE for the top silkscreen layer. Now click OK.
Click Run script at the next prompt and be patient this step make take ittle while depending on the complexity of your design.
Add it to Board
Finally! Open the board editor for the board you want to add the bitmap to. Click that weird-looking add button to the right of the delete X in the tool menu at the left.