Layout images disappear in odd cases

[alexcjohnson]

Two situations where layout images referenced to data can disappear:

• When one of the size parameters is far, far larger than necessary. Normally (with the default sizing: 'contain') the aspect ratio of the image is preserved, so in the rectangle described by sizex and sizey, one of those is limiting and the non-limiting size can be increased indefinitely with no visible effect. This has a limit though: if you make it something like a million times too big, the image abruptly disappears. (this one is from an example by @celia-plotly)
• On a date axis, in data arrays integer numbers and integer strings are both treated as years, but in layout images only integer strings are treated as years; integer numbers are treated as milliseconds since 1970 (and with the local UTC offset no less 🤦)

Here's a working example:

import dash
from dash import dcc
import plotly.graph_objects as go
import pandas as pd

# Create a Dash app
app = dash.Dash(__name__)

df = pd.DataFrame.from_records([
    {"Year": 2008, "Tickets Sold": 8000000},
    {"Year": 2009, "Tickets Sold": 9000000},
    {"Year": 2010, "Tickets Sold": 5000000},
    {"Year": 2011, "Tickets Sold": 5000000},
    {"Year": 2012, "Tickets Sold": 7000000},
    {"Year": 2013, "Tickets Sold": 5000000},
    {"Year": 2014, "Tickets Sold": 7000000},
])
fig = go.Figure()
fig.add_trace(go.Scatter(x=df["Year"], y=df["Tickets Sold"]))
for j, row in df.iterrows():
    fig.add_layout_image(
        dict(
            source="https://upload.wikimedia.org/wikipedia/commons/8/8a/Plotly-logo.png",
            xref="x",
            yref="y",
            x=row["Year"],
            y=row["Tickets Sold"],
            sizex=1,
            sizey=1000000,
            xanchor="center",
            yanchor="middle",
        )
    )

# Define the app layout
app.layout = dcc.Graph(figure=fig, style={"height": "50vh"})

if __name__ == "__main__":
    app.run(debug=True)

And if you make sizex bigger, even as high as 10000, nothing changes. But go up to 100000 and the images disappear.

For the date flavor: add fig.update_xaxes(type="date") and sizex=1000*3600*24*365 (one year in msec), the images disappear. You can find them if you zoom out and back in around year 1970. But if you stringify, ie x=str(row["Year"]), they reappear atop the data points again.