You can make your own, get an AI to do it (if that doesn't creep you out), or grab something from the internet.

PRO TIP: Coloring pages are perfect for this. For our example, I'll use this image I found by searching for "cupcake coloring page."

Step 2: Resizing and .DDS-ifying

Now that you have your image, let's get it into Photoshop.

Create a new Photoshop image that's 512x512 pixels, RGB colors and either a black or transparent background. A black background is the best choice for this but I always forget. Like so:

This will become the .DDS image you'll eventually load into Tattooinator.

Now open your tattoo image in Photoshop. With images I find online, I create a new image with dimensions from the clipboard, then copy/paste the image onto the blank canvas. Like so:

Why not just paste directly into the .DDS file? You can. I prefer to work with the full-sized image so I can tweak as needed. For example, the original has text on the bottom that I don't want being transferred to my Sim's body.

To remove it, I use the rectangular marquee (M) tool to the select just the parts of the image I want to copy.

Next, copy and paste the image into your square .DDS file.

You'll probably need to resize the image to fit. Use the move tool (V) to resize it. You may need to zoom out to see the square "handles" that allow you to resize:

Press [ALT] while clicking and dragging to retain the original dimensions. In this case, I think the cupcake looks cute and fills the canvas better when it's a little wider, so I didn't bother pressing [ALT].

You'll notice that I left a little bit of empty space around all the edges. Any pixels on the edges will "wrap around" to the opposite side of the image. You could probably exploit this to make, say, a barbed wire tattoo that wraps all around the arm. Haven't tried it and I'm not trying to make a wraparound cupcake, so I left a nice little margin all around.

Fill that margin with white.

Step 3: Converting Your Lines to a Red Channel

It looks great and it's the right size, but Tattooinator requires a little bit more to make the image work.

First, let's invert the image. Go to Image>Adjustments>Invert or press [CTRL] + [I].

Note: If you are using an image with a transparent background, you'll need to add a white background before you invert the image. Here's an example workflow:

Then, invert as usual.

I had the wrong settings on my selection tool, so I've got a tiny box of transparency around my image. I colored over it with the brush tool [B] to match the black background.

Now, create a new layer [SHIFT] + [CTRL] + [N] and fill it with pure red with the bucket tool [G]. It's important you use the correct red. Hex code: #ff0000. Tattooinator will use this as the RED color channel.

PRO TIP: Personally, I prefer to use HSB. H: 0, S: 100, B: 100. I know everyone and their pet hamster uses hex codes, but this is much easier when you're working with more color channels.

You should now have a bright red square. Time to turn it into your beautiful tattoo lineart. Add a layer mask to your new layer by clicking the little button at the bottom of the Layer panel with a black circle. A white square should appear next to your red layer's name.

Now, jump down to your inverted lineart layer. Select the entire image [CTRL] + [A] and [CTRL] + [C] to copy it.

[ALT] + [CLICK] the white square to edit the mask data. Your whole image should now look white.

[CTRL] + [P] to paste your inverted line art. Click the red box in your layers panel and you should now see your lineart has magically turned red.

We don't need our original lineart layer any more, but we do need a pure black layer on the bottom. Delete the layer and replace with a black one (or color over the whole thing with a giant brush [B]).

Your image is almost done!

Step 4: Add a Blank Alpha and Save

Time to dip your toes into the joys of Channels! On the Layers panel, click the Channels tab.

Now, click the "Create New Channel" button that looks like a sticky note with a fold in the corner. This will make a new channel called "Alpha" or "Alpha 1" appear.

Click the RGB channel, then the little eye next to the Alpha channel so that all your channels are active and visible. Now your image should look like this:

It's ready to save! [CTRL] + [S] and select .DDS file from the dropdown. Name it whatever you want, pick a file location you'll remember and press "Save."

A window full of exciting options will pop up. Select the same ones as me:

Great work. Keep your DDS file open in Photoshop for now, in case you have to troubleshoot.

Step 4: Tattooinate!

Open Tattooinator and hit the "Select" button next to DDS file. Navigate to your newly saved DDS file and open it. Then, make sure only "Channel R" is checked, otherwise your tattoo might cause issues in game.

Next, click the red boxes on the top row one by one and change them to black or a dark color. These will be the preset "ink" colors for your tattoo in game. I like to do black, brown, and purple. Don't worry about changing the other channels. Here's how my screen looks once I've changed everything:

Click the button at the bottom that says "Preview Tattoo Image." Here's the moment of truth! If you've done everything right, it should look like this:

Viola! Black lines with a skin-colored background. Feel free to click through the other presets and admire your work.

If that's not what your preview looks like, you might have messed up somewhere along the line. Jump back to Photoshop and make sure your DDS image has:

A solid red layer with a layer mask (black background, white lines)

A solid black layer

An alpha channel with just black in it (will show up as translucent red when visible over your image in Photoshop)

Once everything looks good, close the preview, name your tattoo at the top of the screen and then click "Create Tattoo Package."

Save it as whatever you like and place it in your game's "Mods/Packages" folder. Run your game and find your brand new tattoo design in CAS. Congratulations on your custom tattoo!

Personally, I think the back hair adds.

FAQ

I haven't actually been asked anything yet, but I'm a teacher, so here are the kinds of questions I anticipate.

1. I don't have Photoshop!

You can use GIMP, it's free and has basically the same functionality. cmar's tutorial walks through how to save DDS files in GIMP

2. How do I make a tattoo with colors?

You can find the basics of making tattoos with colors in cmar's and WolfoftheNyght's tutorials. They'll show you how to add up to four colors (including the outline color) to tattoos.

I'm planning on making one--maybe--two more, advanced color tutorials. These are for the crazy people like me who want fully-CAStable tattoos with lots of colors. Yes, these are tattoos, not accessories! No, I haven't seen anyone manage this before. (And yes, it's a lot of work…)

3. How do you add .package files to your game?

Sorry, I can't help with that. Check out the Installing a Mods folder tutorial on MTS.

4. This seems like a lot of work to create a pretty simple effect.

Yeah... Thankfully, it gets very, very fast with practice and I'm honestly addicted to creating custom blackwork for all my Sims. It becomes second nature: Grab image>Resize>Invert>Add Mask to Red Channel>Add Alpha and Black Background Layer>Save and Tattooify.

But yeah, the process has lots of weird steps. Welcome to making content for the Sims 3. Haha.